I've heard that AAPS is more sophisticated. I'm definitely not too happy with the Tandem system. Some people say they get better levels with Control IQ, but I don't. The T:Slim does have the ability to set basal rates for different times of day, and takes as input your insulin to carb ratio, correction ratio, weight, and tracks IoB. I don't think the insulin on board algo is very good... it starts decreasing before I see any effect on my glucose, and dissipates quicker than I expect. They base it on insulin lasting 5 hours, I think, but it seems to calculate less time. It's not a 'learning' algorithm either afaik.
The lack of carbs is perhaps the worst for me. Even if I track then on the Dexcom app, it doesn't use them. The automatic boluses are often wrong. When I had it anywhere near my real ratio, it would 'predict' I was going over 160 and automatically dose me. So, say I was at 85, and had 15 grams of potato chips. My glucose would rise quickly and as it went over 125, 140, the system would predict it was going up past 160 - or who knows, since it doesn't know how many carbs I ate. So then it would dose me with say, 1.1 units, which was enough to take my glucose -back to 85-. That sent me in loops a couple of times... 85, eat, up to 145, automatic bolus, back to 85, eat, up to 145 - very annoying when it happened at night. I had to set my carb ratio so high that the automatic boluses are now insignificant amounts like .16 units. It also doesn't notify you on your phone about automatic boluses, which has caused me major problems when I'd also manually correct. The automatic basal reduction (Basal IQ) is useful though.
Anyhow, I'd love to try AAPS but I don't have an Android phone. I also used to follow someone on Twitter who was developing his own software that he said removed the need to pre-bolus at all. Not sure about the details though.