2.35 tires from different manufacturers vary in size. If you want some grippy and beefy tires, the 2.4 Schwalbe Big Betty is about as good and tough as a trail tire goes. You can only go as big as your frame and fork will allow so check that first.
Just be willing to pay more for them as opposed to some $19.99 tires you find on sale somewhere.
Just remember, that the larger tires have a pretty substantial weigh penalty. I was running 2.6 kenda kenetics ( Which were awesome tires) but the extra weight was killing me while climbing. I used to think 2-3 lb really wasn't a big deal until i began reading these forums and asking advice. 2-3 lbs of rotational mass weight is big. You may want to read up on wheel and tire weight (rotational mass) before you spend the money. Of course this is really only an issue if you do a lot of climbing (which in the all mountain forum i am assuming you do), but if your doing mostly down hill buy the biggest tires you can find. I am back down to 2.35 maxxis high rollers and am climbing like a goat.
my bike has 26 by 2.35 size tires whats the biggest i could go? could i go any bigger? i want mountian bike tires
That usually has to do with frame/fork clearance also. If its tight with the 2.35's you probably don't want to go much bigger. Most AM bikes can fit big 'ol downhill rubber though, what are you riding?