Since the machine are all roughly the same price, you have to look at what distinguishes the three machines from each other.
On Pinside's top 100 pinball machines, T2 is ranked #20 while BR is ranked #51 and SG #81. Higher ranking is related to resellability.
The production run on T2 was 15000, where there were only 3746 BRs made and only 3600 SGs. Higher production run usually = more spare parts available.
What you haven't told us is the condition of the backglass, playfield, plastics, and cabinet. I would take a pristine BR or SG any day over a beat up T2.