Sex With Women
I have been with women who found too much length to be a problem as well as those who cannot easily handle much girth. In the first instance it's obviously the man's responsibility to exercise care not to pound too hard or deeply and, as jodyhotwet points out, position can also play a role in keeping a woman comfortable. As for girth it's simply a matter of being patient and going slowly and gently until your partner is comfortable. I had one regular partner whose pussy was extra tight and her orgasms were incredibly intense. I'd always take her through at least a couple of orgasms with my tongue before ever penetrating her for two reasons. First it would do a good job of preparing her vaginal passage for my thickness, and second because the intensity of her orgasm following my penile penetration would always cause me to cum simultaneously with her own climax.
Sex With Men
As a lover of cock I enjoy them in all lengths and thickness, though an inordinately small cock in either dimension can put me off a bit. As my primary homosex interest is oral I do tend to put more emphasis on girth than length simply because I like to feel that I've got a mouthful. Not that I can't handle length as well, my deepthroating skills being well honed, but I'll admit that when deepthroating a cock that is both long and thick I can't breathe while it's down my throat so there is definitely a limitation there.
Forgetting Size
Like most men (and quite a few of the women who frequent this site) there is a very strong visual component to my sexual arousal. So where cocks are concerned my biggest emphasis is neither on length nor girth, it's on aesthetics. The appearance of some guys' cocks and balls will instantly and intensely turn me on, while others do little or nothing for me. That of course is a highly subjective matter, as well it should be. As a matter of fact I think I'll start another thread in this forum on just what visual aspects of the male genitalia appeal to each of us. Is it size, proportions, color, cut/uncut, shaft, glans, balls, hairy/shaved, or?