You need to do a little more archeological digging still. You need to know the whole construction of the floor before you can decide how best to install something new. I'd take up that plywood piece in the kitchen and see what's under it. It's higher than the surrounding floor, so needs to go. You should also be able to see from there what subfloor is under the original kitchen hardwood. It's too bad the space under your entryway is finished, but I'd still do some exploring from below to see what's under there, and to figure out the fix to stop it from squeaking. Is it drywall below or a drop ceiling? I know it probably seems like a pain to tear out drywall, but if you cut out a clean patch, like 2' x the width of the joists, it'll be relatively simple to repair. Just make sure to cut it down the center of the joists so that there's room to screw the patch piece to it later. Cut the hole under the area that squeaks the most, if you can. Have someone walk on and watch the floor from below to see what's moving. It might be as simple as pounding in a couple shims from below, or face-nailing a loose board from above. You want to find out what's underneath the hardwood. It might be laid directly on the floor joists, or there might be 10" wide boards that the hardwood is nailed to. Another thought is to take out a board in the hallway, since that's not original and you want to replace it. See what the subfloor is there. I am a bit puzzled at why, when you've stripped the kitchen down to the original hardwood, it's still higher than the hallway floor. Is your current surface perhaps not the original kitchen hardwood? Peeling back the plywood area will help determine that. BTW, I haven't heard of that stop squeaking product you linked to, so can't offer any personal opinion. And don't pour self-leveling compound over top of hardwood. It needs to go over plywood.

Choosing the right flooring type isn't enough for your living condition. You will have to consider the types of cut: flat sawn, rift and quarter sawn, quarter sawn or live sawn. Quarter sawn and rift & quarter sawn will be best choices, because expansion and contraction is along the thickness of the wood. You will need climate control all year round. 70 degrees at 40 % relative humidity is where you want to be throughout the year. The use of a humidifier/dehumidifier will be needed year round. Although, engineered flooring is more stable than solid. Using the wrong wood specie in your living condition can run the risk of de-laminating with engineered wood. If, the top veneer is more or less stable than it's core and backing. You will experience de-laminating in extreme humidity swings. Take in account of what the engineered flooring is constructed of: mdf or plywood. The width of the flooring will account for how much expansion and contracting also. 2 1/4" strips are the most stable. As you go wider, expect to see more wider seasonal gaps. Proper acclimating is critical, should be performed with a moisture meter. For 2 1/4" strip flooring , sub-floor and flooring moisture should be within 4%. For all other widths 2% moisture differentiation is allowed or should not be exceeded. Don't forget proper expansion gaps, which is the thickness of your flooring, example: 3/4" thick = 3/4" gap. Sub-floor type and condition will affect the performance of wood floors. All this needs to be considered for the proper and successful performance of your wood floors.

Definitely choose wood. Vinyls are great, however, for resale value, wood is the absolute best ROI especially for the main living areas. You can choose an engineered or solid- whichever makes most sense. We are able to provide engineered HW that can be sanded and refinished just as many times as solid. If the wear and tear is something you are worried about, consider choose a floor that has a reclaimed look with a strong grain pattern and saw markings that can hide many of the scratches and discrepancies that will happen over time. If that specific design isn't your style, consider a light color floor. Oiled floors are a decent choice because fixing superficial scratches are relatively easy. Oaks are good because of their graining and if kept a light color- will be able to disguise many of the scratches. You can ALWAYS sand and refinish your floors a few years down the line if needed. Plus, when you go to sell and the floors have been lived on- they can be sanded and finished for the new buyer. A vinyl floor will need to be replaced. Hardwood is more expensive at the moment, but they actually end up paying for themselves years down the line with the proper care and maintenance. Or you can choose wood in the dining and great room and a tile in the kitchen. SJ McCarthy has a good recommendation for hickory and oak. Another option is Character Maple(make sure it is hard maple). If you really want to be bold- go for Brazilian Pecan. :)

SJ McCarthy, our contract is stated we are responsible for the materials and we pay for the labor. Unfortunately we never met nor discuss with the owner but only discussed in details ( in the proposal) with the project manager who is the solely the carpenter.) We just found out there were a lot of the DETAILS from the proposal were not explained (per the PM,but who knows) in detail to the owner or almost like "bait and switch" - for example like item #2- he spent more time because the owner did not get him another helper to help him- I told him this should not be the customer's expenses-Anyway we are willing to pay for it. The owner was offering to renew and establish a new contract from the original contact ( we felt that he cherry picking the items from the proposal, we marked them up then again he decided not to included) for the unfinished works . Once he agreed in our 2nd meeting (another example: he agreed tiling our study room to be included from the original contact in our 1st meeting then when he write the REVISED CONTRACT- he wants to charge us ), but again we are facing the same old stories-he tried to change the wording. We were burned so many times and now we diligently review line by line knowing the owner's personality. He kept saying he lived by the contract-then I told him then he should honor the low estimated to install our engineering hardwood floor including removing the carpet-in the end he says he would honor but he did not including the cost in the new REVISED contract which we add into it - we are so tired with his games. So now we put a contingency - once we agree with the new contract, no more additional expenses from the previous work was done- and we do agree that we need to be notified first and need both signatures for additional expenses from the new contract. and no more point finger of "not included" since we have discussed in detailed and are in the contract. The new addition has a hardwood floor installed - with Dri-core. Once hardwood floor was installed- they are some areas squeak- we were told by PM -put a marked up then he would fasten without explaining to us-these would be additional ridiculous charges (PM told the owner, too-we told PM that they should explain it to us- ) Regarding the installing the engineering hardwood floor is for our existing rooms(concrete slabs that has plywood already)- we are told just to put a vapour barrier. Is it possible to let me know what brands for the glues have to be moisture resistant ($2/sf) or moisture PROOF ($3/sf).? The manufacture instruction suggests to use Franklin Tongue and Groove adhesive (cross linking polyaliphactic emulsion glue) www.titebond.com -any suggestions? This Applachian engineering hardwood floor - FLOATING only needs GLUE between the wood (tongue and groove per the manufacture manual ) then would be FLOAT - this is not to be GLUE DOWN on our concrete floor (could be glue down if necessary but not in our case). Here is the website- on PAGE 9 http://www.appalachianflooring.com/uploads/general/documents/engineered-installation-guide.pdf We trust the PM and we pay for it- we just want to move on and complete the project-It has been almost 10 months. We have to do what we have to do to protect ourselves now- The owner refuses to install our towel bar in our new shower without charging us, and we told him we will take care them by ourselves. I will update this post and hoping for a better solution. Thank you