Yo I'm around your height I ridden both 19.5's and 19's before..Id have to say 19 is my favorite ...I actually had a slammer/detour once, I liked it (the headtube was super mellow tho!!)..My friend had a warpig ..Think warpigs were like 19.75 though..
imo it doesn't matter too much ,dont go crazy, dont get a 17.9" ,or a 21"..
19-19.5 is prob the best bet..