Avoid Briggs and Shiton. Their garbage, I remember taking apart an engine when I was 9, since with a bent shaft it was junk. The cam gear and cam lobes were made of plastic. It's like, really?
For engines, stick to Kohler, Honda, Kawasaki or Suburu. Nothing else. We have a B & S mower from 1992 that still works, but it's never been beaten on in the least. I'd recommend watching out on the HD specials for a Husqvarna mower with a Honda engine. You can't go wrong, and their from the high $300-$500 range. They'll last forever and always be very easy to start. Toro also makes wicked mowers, but those are $$$$$$$
"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs. There's also a negative side"