Bradford White is what I install. You can pick one up at your local
Ferguson.
While you're there grab two 3/4" Dielectric unions.
Swapping a heater out is pretty easy. Im sure your handy enough to handle it Chris. I can do a heater in about an hour. Although I have an awesome furniture dolly and a pump that gets the water out of the old one in about 10 mins. I'd say it may take you 3-4 hours if you don't have to go to the hardware store more than once.
If you buy a whirlpool from Lowes you will require two 3/4" Galv nipples as well (I install for Lowes, that's how I know). Personally I don't think the warranties are worth it, but to each his own.