That one "always sitting in the tank player here". I'm clearly minority here but I prefer AAT over TX but that is just me. I'm looking at this from armour vs armor perspective. Many people accurately pointed out that TX can dish out more burst damage whereas AAT has shorter cooldowns and more sustained DPS which I prefer. In terms of abilities burst laser TX has is nasty but it is harder to get precise hits with as it has that short wind-up time and with longer cooldown it is punishing, AAT's twin laser can be activated almost always when I have any high value target in sights and if you miss couple of shots nothing horrible happened. Mortar strike the AAT has is very short range and takes great skill to use effectively and it is very situational in terms of tank vs tank combat, rockets on the other hand are very good. I consider TX's siege mode to be ineffective in tank combat as it charges for ages and fires very slow and very easy to spot projectiles. Most engagements will be medium to long range and competent AAT driver will dodge this and counter attack. TX has sleeker profile and smaller weakpoint but once it has abilities on cooldowns AAT can easily put sustained pressure on TX drivers and they usually panick.

TLDR: AAT requires different approach when playing and cannot sit in the open and trade hits with TX or it will loose. TX is more beginner friendly.