Great question, but not necessarily something that is easy to answer. Keep in mind that there is no difference in cooking abilities of these grills -- they'll cook the same.
I'll give you a couple of things to think about:
1) How much space do you have? Obviously the Performer takes up more space, so consider where the grill is going to be.
2) Will the grill be moved? The Performer is much more stable when rolling around the yard, patio, or deck. On the other hand, if you want to take it for tailgating, or on a trip, the OTG is a better option as it's much easier to throw in the car.
3) Cost -- how important is that? Assuming you are looking at new grills, the Performer will cost about $175 to $180 more. With the Performer you get the added features of a cart, a place to store charcoal, a table, the gas assist, a lid holder, and a temperature gauge. You can buy the OTG, and add a table, a lid holder, the SS grate (much better than the standard one), stick a thermometer in the lid, use a chimney to start the grill and still have money left over for charcoal and food.
If space and price don't matter, get the Performer. If you see yourself taking the grill with you at times, or money and space are important, get the OTG. Frankly, you cannot make a wrong decision here.