That will depend on a few things.
The main factor will be the rules. If the SD game has 6:5 BJ payouts then the multi-deck games will be much better. If the DD game has terrible rules (H17, nDAS, D9, etc.) then the 6D game will be better. If they all have standard rules then the fewer decks will be better.
Another consideration is the speed of the game. If you are playing BS then you will want to play as slowly as possible. That means you will be looking for the most crowded table available.
Also, you will want to play at the lowest limit tables in order to minimize your losses. Usually the 6D games will have the lowest limits ($5, $3, or even $1) while the DD games may have higher $25 or $50 minimums. Most of the SD games in Vegas are worthless 6:5 games now so you probably won’t have to worry about that unless you're downtown.
In general, look for the lowest house edge with the slowest play.
-Sonny-