I was asked this question a couple of years ago on another forum and I wrote quite a detailed reply. It's still a reflection of my thoughts on the two decks so I'll paste the text here:
I bought the SP10, fully rebuilt, from Angus (Phonomac) when my Sony started playing up as I needed a decent deck to tide me over while Angus was fettling the Sony. So I went from listening to the Sony with my SME V-12 and Phasemation PP-500 to listening to the Technics with the same arm and cartridge.
The Sony was away for around a year so I spent plenty of time with the Technics and found I was really happy with it. It's a very capable deck, powerful, detailed and a solidly neutral platform for the arm and cartridge. No question it's a deck I can live with and enjoy.
The Sony has long been a dream deck for me and I don't know how much that colours my thoughts but on its return I immediately preferred it to the Technics even though I would struggle to say exactly why. To me it's just more engaging. It lets the music flow and I found my listening sessions were considerably longer.
For the last year or so I have really stopped listening analytically. I'm not listening to the hifi any more. I've just been playing records and enjoying the music. I thinks it's because I've got the system to the point where I'm happy with it and I'm not really looking to change anything.
A couple of months ago I was talking to a friend and I was saying that I really couldn't be bothered transferring the V-12 to the Technics just to give it a spin for a month or two. The Technics had been languishing under the bed for about 15 months and I was feeling guilty about its lack of use. I think its important to keep these old decks in regular use. It's not good for them to sit idle from one year to the next. He suggested that I should buy an arm for the Technics and that is what prompted me to get the 3012 and resurrect the SP10.
This is the first time that I have been able to play both decks and I must say the performance of the SP10 / SME 3012 / Kiseki has really surprised me. I thought the TTS-8000 / SME V-12 / Phasemation would blow it away but the reality is that both decks are excellent in their own way.
It's been at least 15 months since I heard the V-12 on the Technics so my memory could be playing tricks but I think I actually prefer it with the 3012. It seems to suit the SP10 very well.
Since I wrote that post I've put the Ortofon SPU Mono GM MkII on the Technics and I'm using it solely for mono listening. It sounds really great. The Kiseki that I mention above is a Purpleheart NOS and it is currently resting.