I made a living doing lawn care for several years.
Snapper steel deck mowers with Robin or Briggs and Stratton engines is where its at. Honda engines are also very good but I don't think they come standard on any Snapper. Tecumseh sucks. The exhaust port covers blow off and not me or anyone else I know ever got a replacement to hold for more than a week.
The Robin (formerly Wisconsin Robin) were two cycle and a lot of Briggs are 4 cycle. I got the same reliability either way. 5-6.75 horse power is what you want.
For commercial use, you want a self propel mower that is belt and pulley driven. Those that use a belt to a gear or a gear to turn a gear that's made into the hub of the wheel wear out really fast. Snapper has always been real good about replacement part availability. They're also fairly easy to work on.
I see a lot of guys using Toro now. My buddy does and he likes them. They cost less than Snapper.
If you get a rider, again, Snapper. I had a Snapper and a Husqvarna. The Husq was big, heavy and a pain to work on. Dixie is supposed to be real good and so is Cub Cadet.
Other small engine equipment
There are two camps here. Buy the best and it lasts. Buy the second best and replace it as needed.
The best is Stihl and Echo. I used Echo. They ain't cheap but they last. They make the best damn weed whackers (string line trimmers), blowers and hedge trimmers. Troy Built isn't bad. Homelite is for home use. They're fine for that. I tried them for commercial use because they were the least expensive and I replaced two Homelite weed whackers sooner than I would have replaced one Echo.
Go with two cycle. Four cycle is too damn heavy to lug around.
Get fiberglass handles. Wood rots out and breaks. The cheapest rake and shovel heads will bend and snap off. It's better to spend more for quality. Screw plastic heads. Get steel.
Gas and oil
87 octane. That is all. My grandpa used 20w50 motor oil instead of two cycle oil. It worked for him. I used two cycle where it was called for and it worked for me. Never mind those high priced super special lawn equipment oils. Go to your local auto parts store and get a name brand oil.