The BK9 was my first, then two BK2's. Fairly recently got another 2 for general use, as one of the three is always in my wife's GHB and the other is geo-cach...er...umm....lost in the woods somewhere. Don't have a 7, but if I had to do it all over again, it would still be the 9 and 2 in that order. Will eventually get a 7, but I can't say I "need" one. There's nothing the 7 can do that either a 9 or 2 can't do, and from what I perceive to be the general consensus around here, the 9 does the big jobs better, and the 2 does the smaller and 'tween jobs as well as either of its more lengthy siblings.
Do you have to choose between the 2 and 7? Would the extra 2" and nominal added weight of a 9 disqualify it for your purposes?
Like most of the rest of us though, you'll likely end up with all three, so either flip a coin if you have to go for one at a time, or do an eenie-meenie-mynnie-moe if you're going to choose between three.
Blues