I prefer him to be invincible. It's one of the things that makes the games more uniquely 'Wario'. Not being invincible also makes it harder to take advantage of the transformations (which is one of my favourite aspects of Wario Land) since on a first play through you can't know which enemies...
Personally I would say
1. Antonblast
2. Wario Land 4
3. Pizza Tower
though the ranking is very close. Antonblast in my opinion has the best soundtrack of the three and doesn't carry the slight disappointment of WL4 moving away from the style of WL2/WL3.
I have Pizza Tower at the bottom because...
Personally I'm not too worried. We might not get it right away, but I can't imagine they'll go the whole generation without a Wario Ware game that takes advantage of the new joycon mouse gimmick.
Wario Land is less certain but I have hope that they'll have seen games like Pizza Tower and...
Sableye is one that could work. It's greedy, purple, goblin-like, and has a gem that's similar to the ones in Wario Land 4.
Plus it's natural inclination towards searching for gems would make it a pokemon Wario would want to have around