Both would look good slabbed. If I have to pick, I'll go with the one on the right. He looks a little taller, possibly a better match for my height, and I think his sizable cock would flop up higher on his belly when I rammed him with his legs over my shoulders. It would be great, though, to have the guy on the left on an adjacent slab so I could look over and watch one of you guys bang him at the same time.
Tough choice, two very very very sexy men! If I really have to choose, it's for the one on the right (more mature cock, something just a little more sexy in his posture). But I'd be very happy with the other guy in my bed too!