Dear Jaspert,
I think both are good choices. I own the AS Mambo and have been very, very happy with it. The Final Tool is very close to the Mambo and its performance should almost be at the same level.
The AS turntables come with the Alpha power supply, which really keeps the turntable speed dead on. This is something you will need to buy separately should you choose the VPI.
The Final Tool bearing is the same one found in their top models and it is guaranteed for ten years. This bearing does not need any maintenance, which was one of the main reasons for me to choose the AS.
IMHO, a high-mass design allows for more flexibility when it comes to selecting a mat, since it can handle heavier mats (SAEC SS-300, Micro Seiki CU-180, etc).
Best Regards,
iSanchez