I would use a straight 30 weight. Follow the mfr. recommendations.

Straight weights hold up better in the rough enviroment that is an air-cooled engine.

You can search for a bazillion answers on this. But the Cliff Note version is as follows:

1) If you're just using mineral oil (i.e., not synthetic), then straight weights have some advantages for protection.

2) If you're willing to pay for a true Group IV or Group V synthetic (a minimal expense on a mower), then you may not even find a straight weight, and it's irrelevent if you do. Get a multiviscosity (I'd probably go 0w40 or 5w40) and enjoy lots of extra protection.

Briggs & Stratton's number one recommendation for any temperature from -20 degrees to +120 degrees is 5W30 synthetic oil, which they sell under their own brand name. They also recommend straight 30 weight oil when the temperature is above 40 degrees. They state that some oil consumption is to be expected if regular multigrade oil is used above 80 degrees.

Honda recommends 10W30 oil, regular or synthetic.

"Also is 30 "HD" ok in place of just 30?"

IMO, it's greatly preferred!
It has a better anti wear additive package.

If your manual says 30W, that's what you use. Regular or synthetic is okay. A very good regular is Quaker State HD30 in the green bottle. An expensive one is Opti-4 30W. A synthetic is Royal Purple 30. 30W oils in general are known as 30 SAE for Society Of Automotive Engineers, and may be recommended on lawn equipment down to 32 degrees F. Honda allows it down to 50F.

I'm going to demur on saxman1's recs. Quaker State and Pennzoil are both made from Pennsylvania crude oil (or were in the past, anyway), which is very high in parafins. They have a bad habit of leaving sludgy buildup, which is probably worse in high-temp situations like our air-cooled engines. Back when I still used mineral oils, Valvoline and Castrol were considered the top of the heap (in the US among major brands, at least).

OTOH, even though Royal Purple comes from my home town of Houston, I can't endorse it. It's a Group III "synthetic," which really isn't a synthetic at all but rather a very highly refined mineral oil. Castrol started that whole sham, and there was a major lawsuit about it, which Castrol inexplicably won. But the bottom line is that these are still mineral oils that require viscosity enhancers to achieve a multi-weight rating (and those additives are what make multi-weight mineral oils not so good, too). The big shizzle about true Group IV and V synths is that their base molecules can be made to act as a multi-vis without additives (they are "engineered molecules, so to speak), and their high-temp-high-shear (HTHS) ratings tend to reflect that. My _guess_ is that Royal Purple straight 30w doesn't have a lot of nasty friction modifiers, but then I think that just makes it very expensive good mineral oil. At that point, I'd recommend saving the money and just buying Valvoline or Castrol mineral 30HD oil.

PS - Even if you get what I consider the worst of the oils, such as Quaker State 5w30, if you use your mower once a week for your personal yard and change your oil annually, your engine will probably never die due to oil problems.

In rebuttal to the above, there's not a thing wrong with paraffin oil - in fact, that's what Opti-4 is, and it is without doubt the finest lawn equipment oil made (and the priciest, but you only use 20 oz a year, so what the heck). I also have experience with the Quaker State I mentioned unde extreme use in a mower with no such sludging.

#1 RULE-Keep an eye on the level and properly filled.

#2 RULE-Change the oil at least once per season or more depending on engine time/usage.

Any brand SAE 30 will provide good lubrication when used properly according to the engine manufacturer, as well as 10w-30 for the same principal. People run into mechanical issues and broken down equipment with shorter life spans when proper and timely PM is overlooked. I for one spend the extra for synthetics, and take PM SERIOUSLY, but as long as you maintain, regular petroleum based lubricants are more than adequate for most applications for the average homeowner.

'but as long as you maintain, regular petroleum based lubricants are more than adequate for most applications for the average homeowner.'

So true.