My LDS is having a promotion and is trying to get rid of a few rental/used regs. Basically, for every new reg ($500 or more) purchased, they will throw in a free used reg to use as a secondary. Two caught my attention, the Apeks AT20 and the SB S550. Which would you take, considering that price, etc. aren't factors. The owner also wants to get rid of a used MK25 (God knows why...) and would throw it in for a very low cost if I take the S550. He said he'd do the same with the Apeks' first stage (whichever one it was sent with from the factory). Highly considering the SB as of now.