Welcome to dirt riding! I wouldn't recommend the CRF150F because of your height--I think that you would quickly outgrow it. I'm 5'7" and started out on a TTR125L--I bought the bike knowing that I was too tall for it, but I wanted a bike on which I could put both feet down flat. I also wanted a bike where I could focus on my riding skills only, and not whether the bike was too heavy or too tall or too hard to start. That said, the TTR125L was fabulous for me to learn the basics--it was lightweight and very forgiving of my many mistakes; however, after only 5 months, I was ready to move on. The low seat height (an inch lower than the CRF150F) was a key problem, both in the "attack" position and when I was sitting (I took the Debbie Matthews motocross class and learned the correct body position for riding). I recently bought my CRF230F, which is wonderful (I can still put the balls of both feet down when stopped), but I think that it would still be too short for your 5'10" height. I would check out the XR250R--the seat height would be better for you (almost 2 inches higher than the CRF230F), and the dry weight of 240 pounds should be fine (I don't have any problems picking up my 238 pound CRF230F from its side, and I weigh the same as you do). I'm not a 2-stroke fan (the powerband is all wrong for my style of riding, and red-sticker bikes are banned from trail riding at OHV parks in California during the late summer months), so I don't have any advice regarding those bikes. I agree with gwcrim's advice above--go to dealerships and sit on all the bikes to see what feels comfortable for you. Good luck, and let us know what you end up with!