Well, if they DID reprint The Best of XY, we'd be seeing Night March/Shaymin-EX returning for another YEAR of play, and nobody wants that except Night March players.
Thats true. Some cards that I would love to see return though, are Xerosic/Startling Megaphone (we really need one of those), Lucario EX (which obviously is not a biased statement), Blacksmith, Fighting Type support Trainers, Manectric EX/M Manectric EX, AZ, and maybe Battle Compressor. Another interesting idea, would be printing Night March Joltik and Night March Pumpkaboo, but NOT reprinting Night March Lampent. This would cap Night March's damage output at 160, and although thats still great, it doesnt hit the magic number necessary without cards that increase its damage. This in theory, would still be reprinting "The Best of XY", while not destroying the Standard metagame.
On another note, assuming next years Standard format is Breakthrough-onwards, some cards that I'd love to see reprinted are Sky Field, Double Dragon Energy, Enhanced Hammer, Lysandre, Level Ball, Hex Maniac, Hoopa EX (and
maybe Shaymin EX... just maybe...), and lastly, both Giratina EX and Lugia EX from AOR.
I feel that some of the 15 or so cards I've listed above would bring far more balance to our current Standard Format and future Standard Formats as well. In particular, Double Dragon Energy is the card which singlehandedly makes Dragon Types playable, and Lysandre acts as an omnipresent but balanced threat (unlike Pokemon Catcher before its Errata). If these two cards alone, as well an item card to remove tools, were added back into the Standard format, I feel 100% confident that the format would be majorly improved in all aspects.