I'm aware that there is no high-end PAL laserdisc player, similar to MUSE... maybe my dead HD-MAC, if working, could have been great, who knows?

Well, back on topic, which is, in your opinion, the best one?

I list the following as possible candidates:
Pioneer CLD-D925
Pioneer CLD-2950
Pioneer LD-V4300D
Pioneer DVL-909/919
Philips LDP600WD
Sony MDP-850D
Theta Data II

I have the first five ones; apart Philips, which is not in use since long time, the others are very similar...

Opinions? Further models to add to the list?

I have the 925 and the 2950, both were just serviced by Pioneer and are back in thralldom, haha..As I´m not able to distinguish their performance I´d give the 925 first place because of the perfect outputs and the 2950 second place, but it gets a bonus cause it´sd much more massive and looks and weight are better.

Is there a PAL version of the Theta Data III? Because that's supposed to be a CLD-D704 under the hood.

I don't have the 925 but the 2950 I own and it's a ripper machine with NTSC playback as well and was a very popular machine in europe

No PAL version for any Theta in Europe. They just have the Euro Voltage power supplies, that's it. Same guts as US ones.

My vote is for DVL-919E/909. These are the only PAL capable players equipped with digital TBC. All other use analog circuitry to align luma. A digital TBC can do this much better and with very minimal loss comparing to the analog version.

Do Pioneer still service machines? How much does it cost?

I think there is a PAL player that everyone seems to forget about and that is the CLD-1050.
I've done a A/B test against the V4300 and for my money the 1050 has the better picture, but not by a heck of a lot.
The 1050 seems just marginally sharper and slightly more detailed.
Both players are way more detailed than the D925, but also show more noise.

Hope this helps.