ST 110 - Investment this is clearly the best book to invest in.
ST 115 - Has some outside interest - early Spidey and 2nd Sandman. Will appreciate in value but not anywhere ST 110 will.
ST 126 - Book is hot hot hot - has lots of legs for sure, if you can find a high grade this one will only keep climbing
ST 138 - Eternity Eternity Eternity, this book is a sleeper, Eternity is everywhere Cosmic stories (Ala Guardians Etc... ) Warlock, Thanos, and if Avengers 3 goes in that direction this will be a Mega Sleeper
ST 169 - I agree with Gadzukes - SEXY COVER - not so much a sleeper anymore but a keeper in high grade
This is just my opinion, but then I'm partial to the Doc.