I've been playing with a variety of RPG / collectible games on iOS so far, and, well,.
after trying a good dozen (chrono cross, blood brothers, rage of bahamut, dark summoner, and many others), I ran into this little gem called "Defender of Texel"
I'd recommend giving it a try:
* Android: https://play.google....257.Dot_Android
Defender of Texel is a RPG / CCG with back to back special events. You collect 5 different levels of fighters (common, uncommon, rare, epic, and legendary) and use them to complete missions, events and pvp. Unlike most games like this, "this one" really stands out because of the nice 2D pixel style art. Over 2 million players so far.
What makes it stand out is that it's perfectly playable without spending a single coin on it. (yeah, im totally cheap like that)
I've managed to compete with the top 1000 (out of 2 mil players that's quite something) within a few weeks of having started the game. It's quite well balanced, the fighters and skills are unique, and the game is receiving new updates just about every single week for the new events. Aside that, the trade system is quite fair (though you do need level 30 - probably to prevent abuse). And, you can upgrade your fighters in a manner not seen in most other ccg like it.
On a side note, if you do give it a try, I'd really appreciate it if you could use the code: "NGaF" after defeating the first boss