Colin
I've got an SP10MKII, it's been used with an Audio Origami refurbed DV505 and AO EPA-100. It replaced a Michell Syncro, other experience has been with that huge battleship Aiwa that was in HiFi world a few months ago.
I've heard a lot of other tt's in unfamiliar systems and I think it's fair to say that a properly implemented DD approach has some advantages, that off the shelf belt drive solutions can't match at similar prices. In the bass, the definition and weight are impressive, the absolute speed stability and somewhat metronomic timing is another key attribute.
On the downside (for a DD), I have found most belt drive decks to have a sense of 'air' or 'liveliness' that I haven't heard from a (My) DD, but this may be a massive generalissimo.
As I have indicated, I think a properly implemented design is key, and in this respect a good belt drive deck doesn't lose out. The Brinkman La Grange (just to pick one) is a great example of this.
Hence, when you are looking at decks, don't rule out the classic Mirco Seiki belt drive units. After the DDX-1000 Micro went on until the late 1980's building belt and DD units with unmatched build quality and levels of engineering which would put SME to shame. Eschewing the three point suspended approach they used mass, air bearings, suction pumps and different isolation approaches in their belt drives. I think these late belt drives may well be a better prospect than the earlier direct drive micros.
This is a source of info:
http://www.my-micro.de/
And here's a picture:
The SX-111FV Belt drive. This has a 10Kg platter, an air bearing and vacuum suction on the platter, sold by HiFi.do for only 180,00 yen!
On the DD side I would also say steer clear of the cheap ones, and go straight for 'upper mid'. The Denon DP80, the Victor (JVC) TT-801 and TT-101 are standalone motor units similar to the SP10MKII and of very high quality. Denon made a plinth for their units but it probably isn't as good as a very good DIY design could be. Don't be put off by the JVC link, Japan Victor Company made some great equipment (the Reiymo transport) and these units are fantastically engineered, (and like the denon, look like UFOs).
A TT101, look at the Vintage knob site for cut away graphics.
Victor TT-101
The Sony TTS-8000 is another option, but often very pricey for some reason. Again, this can be found as a standalone or with a choice of dedicated plinths.
Sony TTS-8000 motor unit
Upper mid still, look at the Marantz TT1000, bad reviews at the time but maybe some plinth treatment would help, looks great though doesn't it? Ask David Price of HFW, he may still have one of these.
Marantz TT1000, 'music link / esotec series'
And lets not forget the Technics SP10 MKI and II. I'd steer clear of the mark 1. The 2 has a better (separate) power supply and is a better deck. I believe the II is fundamentally better than the SP15 and SP25 which aimed to put the MKII package into a more user friendly and cheaper enclosure.
The MKII was sold seperately as a motor unit or with the purpose - built Obsidian plinth (SHB-3?). Further specialist plinths were made by Lead Console, SAEC and Technics. The Obsidian plinth is allegedly poor but I use it with different feet because it looks good and sounds fine to me. I will try different ones later. The SP10MKII's popularity can be part explained by the numbers available, from ex-broadcast units to studio use, many were sold around the world and are relatively easy to buy without going to Japan.
My TT with the EPA-100
Mine with DV-505
You mentioned luxman; look at the PD-444 DD unit and the PD-555 with the vacuum pump. These are so wide it isn't true, saw one recently overseas.
PD-555 with Vacuum Pump