Hello !
I flew only Seneca & TwinCo, not the aztek.
But I would say :
If you fly often enough to be "current", and want a nice speedy airplane, the twinCo is the best.
Yes, not easy to land ! :-) Just need the exact good speed and attitude, what a terrible flare ! And props kiss the grass, you have to be careful.
But that's a greaaat airplane, you will be charmed, the pannel is a mess and there are buttons and switches everywhere, but that smells "the good old fashion twin".
The one I flew was great because you could desactivate turbos manually, which allows you to do some training without stressing your engines.
Problem : de-iced TwinCos are very rare, so you'll probably have a non-deiced one.
Problem 2 : parts may be hard to find.
Seneca I : Great if you want to do some flight training because no turbo, but slow and a bit heavy.
Very reliable, a good transportation twin, easy to land, and a very comfortable cockpit. No Eurocontrol fees with the "below 2T" paper.
But most of them are getting old, quite a lot of flight hours done.
I would prefer the Seneca II turbo (we own one).
But recently built Senecas are too heavy and some even cannot avoid the eurocontrol fee !
Aztek : I never flew, a bit too thirsty, but Piper built reliable airplanes so I assume this one is also a good plane. Maybe parts problems.
About twins, I enjoy the DA42, nice trainer. Too slow and badly deiced for travelling 365 days/year, but nice baby (expensive to buy :-( !!).
Hope this will help...
Frog