Reccomendation Please!

I'm looking at buying my first bike, but I don't really know what's good and what's not. I have no idea what size bike would be suitable or anything. So, I'm here looking for advice.

About me: I'm 6'1, 205 lbs. I have limited experience driving motorcycles; never owned one of my own, just driven friends'. I have extensive riding experience on atv's and snowmobiles, if that help any. I'm also 27, so I wouldn't be overly reckless. I have no intention of doing any racing, especially as this is my first bike. I anticipate most of my driving would be during the day, but with or without light shouldn't be too much of a problem as there's about 21hrs daylight here during riding season.

I've been kind of eyeing something like a yz250f or wr250f, but am open to any suggestions you can offer.

Further Info

1) your physical size (both height and weight are important)
6'1, 200lbs, athletic/muscular so I'm quite strong.
2) How physical / aggressive are you ?
I was a very aggressive atv/snowmobile driver, so I expect I'll be fairly aggressive once I'm used to the bike.
3) what do you plan to ride- MX/SX tracks, woods, fields with friends or ?????
Woods, trails, fields. No tracks anywhere near here.
4) Do you have any riding experience?
Some, but limited. Used to trade off with friends with my quad.
5) Do you think you will race ?
Extremely unlikely.
6) Are you mechanically inclined and will you be doing your own bike work?
Mechanically inclined and I will hopefully do most of my bike work.
7) Do YOU have a preferance to a brand/ motor choice (2 or 4 stroke)? No brand preference, but I despise having to mix gas. :)
8) Do you have a dealer close by your home that you might use and what brand(s) does he carry? Closest dealer is 3hr drive away. Yamaha, Kawasaki, Honda, Suzuki are all about same distance away.
9) How much ($) do you plan to spend on a bike?
Hoping to limit to about $5000. That's Cdn
10) Do you live in California?
Don't I wish...
11) Your age?
27
12) anything else that you think would help form an opinion
Nothing I can think of.