I have three submarines that use engel piston tanks, although none of them are engel subs, and all use a single tank.
I definitely think the TMAX is a more CAPABLE system, I would have no question opting for the TMAX over TAE. It can do more things, but as to whether it is "better" for you depends.
being new to the hobby, you also need to realize that setting up the TMAX is going to be more complicated, and based on what i have seen, you have to be very careful on how you wire it up. Some people seem to have no problem dealing with the engel instructions (i didn't, i found them easy and helpful), but others i have talked with seem to have brains that work in a different, non-compatible way, and they struggle with the engel instructions.
you might consider buying the TAE system, and after you get comfortable with submarines in general, you can upgrade the ballast tanks and swap out the TAE controller with the TMAX controller, and maybe re-use the TAE system on your second sub
it definitely helps that you can converse with other submariners near you. perhaps one of these fellow submariners who has built an engel can let you take a look at their instruction manual and you can decide from that what level of comfort you have with them.