I originally owned a Basis 1400 with a Rega RB 300 tonearm, and I was very happy with that for a couple of years. (It was my re-entry back into the world of analog, after about 10-12 years.) However, I wanted to upgrade to something a bit more resolving as well as wanting to get a table with a suspension, as my little girl loves to dance to the music. So after a couple of years I did upgrade.
I currently use a Basis 2001 turntable, with a Vector M3 tone arm, (and a Dynavector XV-1S cartridge), and I am very happy with it. I have owned the table for about five years now. It is very resolving and has a very, very low noise floor. (And since it has a suspension, my little girl can dance as much as she likes, and I never have any problems.)
FYI: When I first bought this turntable, I could not afford a Vector tone arm, so I bought a lightly used Rega RB 900 tonearm to use as a stop gap measure until I could afford said Vector tone arm. (BTW, in case you don't know, you need to have AJ Conti install a sleeve onto the Rega arms as the standard hole in the plinth is a bit too large.) This original version of my 2001 table sounded very good, coming close to the current Vector's sound. (The Vector is just a bit more resolving and a bit more quiet than the Rega arm. I also like the arm lift better on the Vector as it drops more consistently than either of the Rega's I've owned.)
I have heard the Basis 2500, (with the Vector tone arm), and it is an improvement on the 2001, as it indeed has a bit more very low bass impact, as suggested by Dan_ed. It is not night and day better, but nonetheless it is better. When I get the opportunity, I would like to upgrade to the 2500, but until a good deal comes up, and I have the money, I will happily use my 2001.
I can recommend the Basis 2001 to anyone wanting to get to a mid-level table that one can happily live with for many years. My two cents worth anyway.