Lots of good stuff already covered. OP you mention you've worked with all 3 before so you must have a good sense of the size difference and such already.
I have a large collection of ATBs, have had GTP in the past and my bf/dad have some ETBs.
Temperament is varied per individual but in general, ATBs are going to be the most bitey of the three. Bite first ask questions later (they also musk). They are also the most active of the three species IMO. Adult ATBs can be kept in 18" and 20" cubes as adults (or bigger of course!). I had my GTP in 24" cube, ETBS will need more space as they are quite a bit larger. Of the 3, ATBs are the cheapest, nice CBB for anywhere from $100-500 depending on color and morphs average about $1k. GTPs and ETBs nice CBB with lineage will easily go over $1k. I would avoid WC/LTC if possible.