I'm a feline with a canine. It makes a great pairing for us. Though we also both like the blend of wild/domesticated, which may explain a lot. He's a fennec fox/corgi and I'm a rusty-spotted/ragdoll cat.
My mate's not a furry exactly, but he's told me a couple times that he wishes he could be a chipmunk and I've been given permission to draw him as such. I've seen it firsthand, Umbreon + chimpmunk = adorable together. ^_^
Different furry species matting or just being with each other is a lovely fantasy; which means that the idea of a certain combination being better than others in also a fantasy; a personal one. That means that the person you might be trying to ensnare might have a different idea for a perfect combo.
It's alright to take species into account when you're looking for someone, but never... ever... should it be your priority number one.