I think the Aztec is the better aircraft, but it does depend on your mission profile.
The Aztec has the virtue of being almost bullet proof. Throw everything at it and the kitchen sink, add in some hard IFR weather and a grass runway and it will keep on smiling.
Add to that the feel of a "proper" aircraft, infact almost a mini airliner, and you can feel you are entitled to the gold braid (well almost).
The trouble is it is as hard to find a really good one as it is to find an MP with an honest expenses claim. Even if you do, the avionics will be antique.
That said there are very very few singles that will compete with an Aztec. There are a few that are faster, but done will carry the load and give you the same piece of mind as the trusty Aztec.
As a mate of mind says, when asked what would be better than the four engines on his 47, with a wry smile, he always says he wished he had five.
As twins go the Aztec is almost vice free. Perhaps a tad of care for the engines doesnt go amiss, the cowl flats are there for a purpose, and a mite of care on wet grass with a cross wind, but the handling is more benign than the Seneca and the build quality better. Single engine out is a complete non event.