Actually, I got the impression that Ginny is the only person that Harry can possible have romance with.
Hermoine is definitely out of the question because JKR gave us clues over an over an over about H and R getting together - the only reason why she doesn't want to confirm it is because she enjoys all the fan theories and such.
Cho - hopefully we are done with her for good ^^'
Luna - he doesn't know her that well, nor did she ever express any love interest in him
Ginny - had a huge crush on Harry but now she grew up and handles herself much much better. She does date other guys but it doesn't look like she is serious about them. I think its more for fun. And think about it - she has been introduced to us from book 1 ^-^ She has to have smth big happening on her part. Harry wasn't interested in her at the beggining because she is more of a kid.
Lol.... and for the last choice....
Moaning Myrtle!!! hahaha!!! she does like Harry...ALOT....XD lol