You battle with three at the same time. Your monsters in queue is limited at the beginning of the game, but it’s expandable. Your inventory is unlimited.
So yes, basically what everyone has said already. ^^
Pegasion!
I won her from my first gold egg and she just made my gameplay much more enjoyable, I haven’t had to do any slow grinding (which I imagine without her I would have) her design is stunning and Luminate is probably one of the best moves in the game :P
Honourable mentions - Meowzard, Luxknight, Blazerunner.
Now that’s HI is released:
I love Archeonis. I must admit that it’s not the most powerful, but it’s pretty good!
Second favorite: Pearex/Raptorex. The first evolution is adorable and strong, the second is cool and strong. A keeper for sure!
Third favorite: Sanders/Kentucky. I am not joking. It has a good passive skill (stun skin) and stun gift. It’s my favorite stunner, but once again, there may be better ones. But sanders/kentucky is so ridiculously easy to get. It may not help you in PvP but in solo-play maybe three to five of these guys will help you beat difficult missions with a lot of bonus attacks.
Now that HI is released:
First: Leviathan
It’s relatively easy to get and, once levelled, the deluge attack is incredibly powerful
Second: Ventowyrm
Not the easiest to get, but it’s powerful and looks amazing!
Third: Dreadwolf
Very hard to get but it has some fantastic attacks and it looks amazing.
1st - don penguini
2nd - Kentucky (absolutely under rated)
3rd - angelon
These 3 characters form the back bone of my pvp final 3. I came back numerous time winning when I am down with the opponent having 8 standing by.
I love it when I win against players having nearly all s grades and power houses like omega, snowja, etc
- Arkwing
- Dreadwolf
- Magmawyrm
Also, I don’t know where this fits. It probably goes between two and one…
BREEZELING.
GOSH GUYS HAVE YOU SEEN THOSE ADORABLE CUTIES?!
You gotta choose, Reset. Who will be the new Piccio?
BREEZELING BRUH
Ughh! But Sanders is so close.
BREEZELING
SANDERS
I CAN’T
I’m looking for a way to fight with breezelings. They seem very fast, so maybe that’s a start.
My favorite is, without a doubt, Ironheart.
WHY NO LOVE FOR DON PENGUINI??
So, first of all he’s a penguin. Which means its like 50x better than any other arky.
Second, it has a hat!!
APENGIUNWITHAHAT!!!
It’s smoking a cigarette.
It has a cane.
It’s a penguin.
It has a hat.
It has an epic trench coat.
to put it in short, you don’t want to mess with don Penguini
Minespider and dreadwolf
Triphoon and Cyberwyrm.
Isn’t it unreleased? I thought you weren’t a beta tester.
Anyway, mines skull wraith
He’s dream hunt and roulette are sooo cool
Maybe he just likes the appearance. Or has experienced their awesome through Ashley. Or both.
Hmm I like dreadwolf and omegawyrm
If we were talking about geomon that would be different i love everything 
Correct.
Correct.
Those are nice moves.
Nailed it.
Bloodclaw
In apperance
#1 Cyberwyrm
#2 Hydrowyrm
#3 Angelon
In power
#1 Typhoon wyrm (only fusion wyrm i have :p)
#2 Arkwing (this guy is serious kick ass)
#3 Angelon all the way B) this guy is uber strong
And i have to put dreadwolf up there 
even though hes not in my top, i love him enough that i had to through that out