Provia 400X has a warmth without too much colour push http://www.flickr.com/photos/d1v1d/4619467743/
I like all the Fuji Pro. slide films, but tend to use more Provia 100F and 400X in 135 and 120, but have also had some breathtaking results with Velvia 100F in 120.
Kodachrome. Always. I am now trying the Elite Chrome and Elite Chrome Extra Color in ASA 100. Kodachrome will always be the best, though. I have some vintage obsolete films in the fridge that I need to try.
All the Velvias are my favorite, then E100G/VS, the Provias.
Didn't care for the Elite Chrome at all. Especially the Extra Color. The Ektachrome E100VS looks much better to me. More like what I expect. Not quite Kodachrome, but nothing ever will be.
I mainly use Velvia and Provia, but I've just purchased 10-rolls of the outgoing Fuji Sensia 100, so I'll be using that for a while. I've used a fair bit of Sensia 200 (rebranded as Boots) and have been fairly happy with it.
I just got back some Efke IR and T-Max 100 from Dr5. They make for interesting slide viewing, especially in stereo. T-Max out performs the Efke. Something fun to try if you get bored.
If you can find some, I shot some Kodak Lumiere. Really outstanding stuff. I won't say anything snotty about it being so good Kodak discontinued it. I want to, though.
Stereokodak I've also enjoyed dr5 process shooting stereo. I have a stereo realist and Rbt s1 my favorite film is efke 25 really sharp and grainless beautiful in a red beautiful in a red button viewer. I recently bought a leica p 2000 with 90mm color plan. Seeing the slides projected is really stunning Nik
The grainless provia is nice, but I find it a bit less sharp than Kodak (more grain). I miss you, Lumiere. Now I use Kodak E100.
I'm still finishing off the last of my Sensia 100 and 200, which was great for the money. Great exposure range. I liked Astia's color palette as well, but for the cost difference I couldn't justify shooting it in quantity. Elite Chrome 100 seemed more contrasty to me and rewarded more careful exposure. I did enjoy shooting Kodachrome 64 and 200 while they lasted, and Kodachrome 200 seemed better than its reputation. 64 really was fantastic. Of all the slide films I've tried I've only found the quality of Sensia 400 to be distasteful, but I expected it to have significantly more grain out of the box.
Velvia 100 for flowers & landscapes. Provia 100F for other color slide work.
PKM/KM/PKR/and KR were my slide films of choice for over three decades. With the end of Kodachrome, however, I have switched to E100G/E100VS in both 35mm and 120 formats, depending upon what I happen to be shooting at the time. Now, with the discontinuation of EK's E6 line, I will have begin anew, and start checking out the various Fuji E6 emulsions...after I have finished shooting the stash in my freezer - say in about two years' time...