Looking to expand my book collection (need advise)

HI,I am currently looking to pick out a new book for Xmas.
I own all 3 HOH, the new 6max book and Little Green book audio.
I am torn between Sit 'n Go Strategy by Collin Moshman and the theory of poker by sklansky.
I was originally all gun ho on buying the sng book,but after some research I keep running into opinions that say cash games are more profitable?I currently play 90% 6max 2nl cash games but was thinking of making the switch.I really enjoy playing the 6max stt at stars and find the micro games super soft and with even more donks then at the ring games,perhaps sng's just fit my style better?Ideally I think I would like to make the switch over to sng but do not want to cut myself short.Any opinions on this would be greatly appreciated.
The other book I had in mind was Theory of poker due to all of the must have reviews found all over the internet,or any other books you guys feel would be a good fit for the beginning player.Any and all opinions would be greatly appreciated as I'm chomping at the bit to pull the trigger on one of these. (no money to buy them both right now) Thx

SNG strategy is very good.

I chose to read no limit theory and practice rather than the theory of poker. I think the base concepts developed in both books are the same but theory of poker takes a lot of different poker games as examples while no limit goes more in depth into NLHE. Lots of poker math in there, essential read.

They're all quite easy to find...

Yea,the only thing I find some what confusing with the 2+2 book is that alot of the tiles seem so similar?I'll be ordering from Amazon so finding the books should be no problem and open to any opinions.

I believe Moshman's book is very good if you want to go the SNG route. That's where I started because I heard the quality of play was very low and because I kind of liked the competitive structure of the game. Though to be honest, I think most of what you'll find in that book can be read in the SNG forum sticky digest/Beginner's digest. All of the examples are nice, but then that's what threads and tournament reviews are for. Still, it's nice to have something to read when you're not at the computer.

I guess I'm going in the opposite direction as you though, because I switched from SNGs to 6max because I felt like it would let me get involved in more hands with more flop play in marginal situations.

I checked Theory of Poker out of the library but haven't read it yet, as I understand that it's somewhat basic and dry, and doesn't focus specifically on NLHE. I was careless when I placed the hold and thought I was checking out No Limit Hold 'Em: Theory and Practice, which is what I really want to read.

Anyway, speaking of the library, it can be a good resource if you're having trouble deciding what to get next. Obviously this depends a bit on the quality of the library in your location (here the library system is pretty good, and there is an interlibrary loan system where you can request books that aren't in the local system).

Sklansky's books are not easy or fun to read, they're indeed pretty dry. However, no other book I know of (barring Spoon's threads) covers so thoroughly the math of EV, equity, odds, etc which are all essential concepts to master for cash games.