Hey Vinitine, never mind ^^ that dude. The Beginners forum is for asking questions, so stick around.
Are you looking to compete eventually, or is it just for your own personal goals/guidelines?
So you know what you "should" be doing, but you've just fallen off the wagon?
How have you been training and eating most recently?
Is your knee 100% healthy again? Does it prevent you from doing any type of training (lifting or cardio)?
Your profile says you're 5'11" and 273 pounds. Is that accurate?
If so, the best weight to get to will be whatever actually leaves you with a good amount of muscle, since you said you didn't have much muscle even when you were 100 pounds lighter, and still have solid conditioning/endurance.
Depending on exactly how fat you've let yourself get, there's a very likely chance that you'll have to drop well-below 200 to get rid of enough useless bodyfat and get into "fighting shape". Have any recent pictures?
The strength issue is a whole 'nother topic, because lighter weight classes can be just as strong or stronger than some heavier dudes. But really, that's a side topic and something you can see frequently discussed over in the Combat forum here.
I think the best bet, depending on how you're currently eating and training, will be to get on a fat loss diet and targeted fat loss training plan right away and let the progress take you where it will based on how your strength and measurements are turning out.
So consider spending a few months just getting back "in shape" and then start thinking about narrowing down a particular weight class.
But just to throw some numbers around: Georges St. Pierre is 5'10", walks around at 200 and fights at 170; Rashad Evans is 5'11", walks around 220ish I believe, and fights at 205; Roy Nelson is 6'0", walks around probably 270-280 and fights at 265. They, obviously, have different physiques (ripped, soft, and fat, respectively) but they're all around your height and perform great in the cage.