What type of bike should I buy?

Best fit is found by going to an actual bike shop. At 6' 4" tall you need a bike with a large frame size. Discount store bikes only come in one frame size. And if the bike trail is paved, you won't need a mountain bike. A hybrid would fare much better. The 700c size tires roll easier with less resistance vs. knobby mountain bike tires. Since I'm a big Diamondback fan, check out these two. One is a hybrid, like I own. The other a 'dual sport' bike.

http://www.diamondback.com/insight-2-pavement-perf... - Hybrid

http://www.diamondback.com/trace-sport-mountain-du... - Dual Sport for on & off road

Your problem was the wrong size bike. Go to the local bike shop and tell them where you want to ride. Sizes vary between manufacturers so you need to try them first.

Google bike shops + your zip. See what they sell and then go to the manufacturers web site.

Edit:

If you can put a bike together take a look at Bikes Direct. You may be more comfortable on a 29er. If they don't have a recommended size chart measure your actual inseam not you pants inseam. You want the stand over height to be 2-4 inches less then that.

http://www.bikesdirect.com/products/mountain_bikes...

A Mountain Bike Downhil Mountain Bike like a Trek Session 88,the Trek Session 88 was made famous in the Trails with the Dog chasing it.

Go to a bike shop. Go to a bike shop. Go to a bike shop. Walk the dog, he needs it. Ride the bike, you need it. Don't mix those two activities.

i would DEFINETLY reccomend either a Giant Glory 0 or a Giant TCR adanced sl 00