Well, one solid theme deck you can get is:
GE Darkrai. Why? It comes w/ Roseannes research, a staple supporter. 2, it comes w/ 3 different kinds of energy, which is very rare in a starter deck. 3, it comes with a 4-2-1 Beedrill line, w/ GE Weedle AND GE Beedrill, which is very helpful to build Speedrill, a generally cheap, fast and awesome deck.
The second deck you should buy is:
SV Milotic:
It comes w/ Cynthia's feelings, AND Roseannes research 2 staple supporters, and it comes with some SP pokemon which are good for beginners, cause they are easy to play with at league to get used to the concept of SP. Then, you should go out and buy RR packs, as they contain RR beedrill and Luxray, one of which is incredibly rare, the other of which works in beedrill. Now I recommend these 2 because as it stands right now, you can almost make a full beedrill buy just buying those theme decks and then going to league to get Uxie and Claydol, both of which are used. Beedrill is fast, easy to use, fun to play and just an all around good deck.