I won't lie, I had a kink for real mares since I was probably 10; something about the large female posterior on the mares appeals to me, but the body types I'm favoring are the slightly-heavier types like the American Quarter Horse and the Suffolk Punch, with slightly shorter legs that make their bodies look longer. That's part 1. I'm also seeing her in my head visual with a chestnut coat color.
Of course, there is the attraction to women, so that would make it part 2. As I'm a severe boob-fiend, of course I will be lusting for large naked breasts.
Combine all those points into one creature: a beautiful woman from the waist up, but from the waist down she's a large creature with a big, round ass on her. I would also fantasize her having 2 sets of mammaries; her human breasts at the top, and mares teats between those large thighs of hers.
A conversation with another artist about 10 years ago described the personalities of centaurides being far more affectionate than the males, and that they would prefer human males as partners as they were capable of reciprocating affection far more than male centaurs would. Instantly, I had the mental image of a young man doing a slow massage on a centauride's posterior before he consumates the "union," and her just laying there enjoying it.