Hi Emptyjar from the C&V forum too.
I have a Diamondback Sorrento and an 800 trek. They are both good bikes. The Diamondback I got at a police auction about 20 years ago and its by around town beater. Its worked well and all I have replaced was a BB cartridge when I got it.
The Trek I rescued from the scrapheap for $7 missing a rear axle and a seat. AN LBS gave me a bagful of hubs and I relaced the rear wheel to get it going again. I think the Trek is a Better ride.
Size- I think ragingbulls sizing is shorter than it should be. I'm 6'4" so I always look for a XL size of anything. Poke around on the brand you are interested in website and find out what they recommend and what sizes they actually make.
2 years ago I got a used Diamondback 29er that works better on singletrack (I think) than my older bikes. I also like the disk brakes MUCH better.
Have fun!
-SP