1) 6'5" 185lbs
2) very aggressive
3) MX/SX tracks, woods, fields with friends
4) have experience on 4wheelers and sleds, none on bikes
5) wont race
6) Are you mechanically inclined and will you be doing your own bike work? -- No
7) Do YOU have a preference to a brand/ motor choice (2 or 4 stroke)? -- No
8) Do you have a dealer close by your home that you might use and what brand(s) does he carry? -- Buying used, private sale
9) Have 1200 to spend
10) Do you live in California? -- Live in Maine
11) 20
12) anything else that you think would help form an opinion -- No

Your options are very limited at that price range. It is hard to find a bike for $1200 that doesnt require work. With that being said, I think an older 125 2 stroke would be best for you. A 250 2 stroke would be alot of power for your skill level and a decent 250 4 stroke will probably cost you more than $1200 and require more maintenance than you are capable of (according to your information). You may want to save up some more cash or teach yourself to work on bikes...just my 2 cents.

Thanks