Marvin Ultimate is a wood frame rather than fiberglass. Its more expensive than Integrity overall and there are mixed signals about the longevity of cased wood windows versus fiberglass or vinyl. Marvin is as a whole is very highly regarded tho and they are the producer of both lines. The Ultimates have more customization options over fiberglass Integrity. There is just some things you can't easily do with fiberglass as compared to wood. For example, our home is going to have some gothic arch top windows. I couldn't get them in Integrity and had to again go Ultimate for those particular windows. And believe me, they aren't cheap (probably due to the custom gothic radius). But the outer colors coordinate between Ultimate and Integrity so it will hopefully be a flawless mix. Windows aren't installed just yet or I'd post pics. I wouldn't believe white painted interior on the wood ultrex would be any less clean looking than all ultrex assuming whoever is painting knows what they are doing. I'd definitely track down a showroom and compare the two lines side by side. With the Wood ultrex its just a more classic looking window profile I think. The all ultrex is quite plain and almost, I dunno, cheap looking in comparison. Its definitely the more durable option tho, no paint to scratch (although the fiberglass can be painted) or wood surface to ding... Its a judgement call for you really. The Ultimate sliders come in 4 panel yes, in 10, 12 and 16 feet wide it looks like straight out of the catalogue. OXXO configuration so the 2 middle sections open to form one opening and net clear openings here listed in my catalogue lead me to believe if both are open, there is no obstruction in the center. The 12' wide one has a net clear opening value of 57 7/16" (or 59 for the non french door) The ultimate sliders have 2 versions..basic patio door and french door. The french door version has wider rails framing the glass, to mimic the look of a french door. The basic version has more glass area and thinner rails so if you go that route make sure you choose the model you prefer To throw more choices your way they do also have these in 3 panel like the integrity but in greater widths. I see here a 12' three panel as well if you just want one active slider but a little wider than the 3foot operator of the 9 wide integrity..lol What you should be looking for to find out how drafty these types of doors are in order to compare them to each other is air infiltration values. Unfortunately with Marvin these can be a bit of a hassle to come by but you could take numbers from a similar manufacturers slider and compare it to your lanai or bifold doors to maybe get a rough idea.

We originally had a slider spec'd, but we would prefer to have a door that opens all the way. My main concern was cosmetically that the panels would be too narrow. Was hoping to get an idea from those who have installed or own a similar door if 33-34" per panel is too narrow, especially at the taller 9' height. It's so hard to find pictures and examples of anything other than 12x8 or 16x8 it seems.

Thanks for all your comments; very helpful information about the screens. I am also overly rodent sensitive as we just finished ridding ourselves of those that we found were living in our recently bought house. Before that ordeal, I wasn't thinking about the bi-folds much, but now I am definitely very cautious about it! Although I haven't seen them in the yard yet, it is apparently common in the neighborhood so its just a matter of time. Plus we haven't moved in yet (awaiting this renovation to complete). Having gone through the options with screens, I am leaning towards concurring with Patricia that it takes away from the wall's openness. Which means, with my rodent sensitivity at this point, maybe a fully open-able wall is not right for us. Having fixed glass panels would still provide the visual openness we are looking for, most likely. Thanks again for your time, all!

They both have pros and cons and neither is really the "best". Budget, sizing, how you intend to use it and what you want out of the door opening all factor in to the decision. Budget and brand do as well as a cheaper folding door will be more like to have issues than a cheap sliding door.