I fish for Smallies a whole lot. I use a 5 most of the time but a 6 part of it. A 7 a bit more than the 6 and sometimes an 8. Given your choice I'd go with the 7 not because I use it more, cause I don't, but because I always opt for the bigger rod. A seven will not let you down With bigger poppers, or more importantly in wind.
Someday in the future if you want to get a few more rods you can always get the 5 and 6 weight rods. I just think it's better to be overgunned than under gunned.
P.S. I almost forgot, welcome to the forum! By the way where are you located? Oh, and check out the Smallie in my avatar.