Depends entirely on what you want out of your tablet. And there are multiple Zenpads, you'd have to be more specific. I do know ASUS puts their skin their tablets, and while smooth enough in day to day operation, their update prospects don't look very good. I can't remember if my friend is still on 5.0 or if he actually got 5.1. I know he doesn't have Marshmallow, and those tablets are locked down and varied enough that the community for them isn't very large at all.
However, in the sub 10" form factor, I honestly don't think you can beat the Shield Tablet K1. Pair it with fast mSD card, and storage shouldn't be an issue.
If they weren't so old, I'd recommend the 2013 Nexus 7 (I have this tablet), but for what they sell for, the Shield Tablet K1 is the better recommend today.
I almost bought the Shield Tablet K1 (the full name is important because there are two Shield tablets) because an idiot relative water damaged my N7, but I was able to find enough parts to attempt a repair for half the cost.