I suggest some more homework before you decide.
While they're both B's, the B3000 is an older model, the B2601 is relatively new, current model. I have a 1953 tractor; old is not a bad thing...
I think (?) the 3000 is 4 cylinder vs. 3 for the 2601. I know a guy with a B3000 with just a MMM. Thing is a bullet-proof beast....know nothing of it other than that, except it was his first Kubota, and now he has 3 or 4.
I know nothing practical about the B2601, other than I shopped for one myself couple years ago. While I love my BX, I should have bought a "B" 5 years ago...Lot of guys here REALLY like their B2601's...that's an important testimonial.
I'm just thinking while similar, the technical differences of the 2 may be like comparing apples to oranges...not sure of that, but worth looking into. I'd look for weights, tire sizes, PTO HP, FEL lift capacities, etc.
I'm assuming you're looking at used....service histories, storage inside/outside, types of use, hours, etc., all also come into play.
Try starting here:
http://www.tractordata.com/
Best of luck in your endeavor! I'd be interested how it goes!