I am thinking of buying my first ATV or Dirt Bike this summer.  I have never owned my own, but have rented a couple ATV's at the sand dunes.  Because I am such a big man 380lbs I want to know what size would be sufficient for me in either an ATV or Dirt Bike without being so overpowered that I will kill myself being that I have limited experience.  When I rented the ATV's at the beach they were Honda 400EX models that did pretty good but I still felt I was wearing it down maybe it's just me.   Also I was wondering the difference between a Off Road bike and a motorcross.  I would mainly hual it to the beach and mountains to ride so which would be better for me.  I know that Motorcross bikes generally are two stroke, I don't even know if you can buy those in CA.  Any advice or links to good advice would be greatly appreciated being that I am so ignorant on the subject.  

you can't buy a new 2 cycle anywhere.

a yamaha yfz450 would do you well.
or the honda 450r

the raptor 660 or 700 would really do ya well.
but as you said may be too powerful for you.

if you are going utility try a 500cc
just watch out for the polaris they have a bad habit of breaking down on ya.

and polaris' have a really bad record for poor quality, poor built atv's
even had people seriously injured when the transmissions locked up, or the steering stem broke. they even had recalls for the brake calipers falling off.

and some of the polaris machines legally fall under the category of "lemon atv's"  

I keep getting those comments about Polaris.  I was looking at a Bombardier (Can-Am) 800 HO 4x4 It kind of seemed a multi-use utility/sport atv which would be perfect for my needs what do you know about those or similar.  Also people have suggested a Rhino or Predator ??? I'm ignorant on those.  I have looked at the Raptor and I like them.  I'm not afraid to have the power for when I get more experience, but that Can-Am bike has really peaked my interest because I would like something I could use hunting and on trails and still take down to the dunes.  

I have heard alot of complaints with the can am that the frames were weak, with that being the case you wouldn't want to jump it much, and you'd want to watch rough terrain.

Polaris just doesn't care about their quality they only want to make a fast sell. and when it comes to warranty you can count on them to tell you no.

the rhino is a side by side.
which is basically a mini atv/truck
and side by sides can't be ridden everywhere.
there are restrictions for width on most orv. trails.
Of course the rzr and ranger being a polaris, honestly you don't want to buy anything with the polaris label on it... unless of course you like pouring money into an atv for constant repairs.

However i am an atv guy. i like riding atv's more than any other offroad vehicle. you just can't beat the manuverability and sheer fun.  dirtbikes are more manuverable but eaiser to wreck. i rode dirtbikes for years, and i think i actually wrecked everyone i ever owned too. alot of fun though.

i think you'll love the raptor once you get it.
absolutely an awesome machine!  

What about the KTM quads?  Are they quality? Do they compare at all to the Raptor?  I'm not familiar with teh KTM brand.  

yeah ktm's are nice, but they are like strictly racing just like all there other dirt bike models. And wolf1, yamaha still make their 2 stroke 125 and 250's, along with ktm has tons of 2 stroke bikes. If you want something that haul u around the mountains/woods get a brute force those things are as big as a freakin jeep hahaha