Well, right now, it's all repeats! So, shameful to say, the best for me is current "So, You Think You Can Dance?". Go ahead, shoot me, I understand...
Last month, though, the best show on TV was a big tie between Charmed, Smallville, CSI (all three of them), Numbers, and Veronica Mars. I don't know if or when the show will return, but Nip Tuck usually becomes #1 while the others are repeating.
There are two new shows coming next month that I am extrememly excited about, hopefully, for good reason. They are Blade (starts next Thursday on Spike) (I absolutely love vampire movies and TV shows, expecially the ones with karate vampires!) and Hex (I think it starts June 28th on BBC America).