This is certainly a toughie.
I have been a long-time fan of CSI Vegas and probably still would be if they hadn't gutted the cast... but now that Sara, Warrick and especially Grissom are gone, I haven't been able to bring myself to watch. Taking Grissom out of CSI Vegas is sort of like taking Mulder out of the X-Files - it just isn't the X-Files anymore. It's something similar: it's a pale imitation of a once great show that depended on the presence of a great character. As a long-time X-Files fan, I could see how the show rapidly deteriorated despite the inclusion of a new agent played by a highly recognizable actor. I hope the same doesn't happen for CSI Vegas (Lawrence seems to be popular so far) but even if the show pulls through this setback with flying colors, I won't be able to appreciate it in the same way as before.
I've gotten into CSI Miami over the past couple of years and I've come to absolutely love it. The thing is... I love it in a completely different way than I loved CSI Vegas. I watched CSI Vegas because it was intelligent, it was intriguing, it was well written, it was well acted, it was well directed, etc... and oh, yes, there was some great shipper material as well.
Here's the difference - I watch CSI Miami purely for the mindless entertainment value. The plots are usually paper thin and occasionally positively ridiculous, the lighting is all sorts of wonky (the first few seasons had the lab shrouded in almost complete darkness and then the later seasons have the lab lit up to the point that it glows like neon), the characters provide unnecessary verbal breakdowns of their tests and procedures to each other as though the other members of the team don't already know what's going on, the writing is mediocre and often downright cheesy, and Horatio has turned into a cartoonish caricature of a one-liner-spewing bad-ass.
But I LOVE CSI Miami. I love it love it love it! I love it despite, and sometimes BECAUSE of, its flaws. Plus, I am SUCH a sucker for the Eric/Calleigh pairing. :adore:
Oh, and I've never seen a full episode of CSI New York (except for the CSI Miami cross-over).
So...... I guess, after far too much babbling, my order of preference goes like this:
(1) CSI Miami
(2) CSI Vegas
(3) CSI New York