If you're going for a minigames server and lots of players, MiNET is probably you best option. Just know there aren't any public plugins yet.
If you think you're really gonna have a lot of players and you don't want to split your server into smaller servers, I would go with MiNET. Just know you'll have to code your own plugins C#. If you want to stick to PocketMine however, you could always just split your servers into more than one server with shared inventories and everything.