I agree with Tony. Those big Menghai recipes are good now (if you like that strong flavor) and will be great to hang on to. Same with the XGs.
I'd get one or two shengs... maybe one of those Tony mentioned, plus maybe something a little more along the lighter "drink now" lines (such as a Mengku)..
and one or two shus.. something that has been recommended in the forum.
I kind of agree with "a cake is a sample," but it depends on your intentions. It never hurts to have an extra cake around that you're not going to drink for a few years.
There's nothing wrong with buying small samples either, but it's more $/g. That's how I got started though, just buying lots of small samples to get my feet wet and get familiar with a bunch of different sheng and shu flavors, without breaking the bank. (Even that is much cheaper than a daily latte.)