Sorry if there's already a thread like this, but no one seems to be posting in it anyway. Anywho, the question is in the title! Use a similar format, please. Here's what I think:
Best:
Dragons, because they're easy to train, very loyal, and awesome fighters!
Zans, because they're scary strong, very fast, and really accurate. Plus they get a lot out of the training.
Tigers, because they're fast and accurate, and they have some strong attacks.

Worst:
Plants, because they're very weak, slow, and inaccurate. And they're not very reliable.
Ogyos, because they're weak and inaccurate, and they get hit with a lot of attacks. What's worse is that they fail too often in training.
Gitans, because they're weak and take lots of damage from lots of attacks, and they fail several times in a row! Not to mention very, very inaccurate!

I would have to agree with you on the best and worst monsters I like the looks of Gitans but their so annoying.Also I always raise Mews and Suezoes and they seem quite good and my sister raised at least 13 Tigers in a row she loves them and they seem good.

I can train almost any monster to be a champion, especially the ones I already mentioned for the best. It's just Ogyos, Gitans, and Plants that don't work!

The lack of strength in a monster is the lack of strength in a trainer. I trained an Ogyo and it defeated the whole game including the monster at the end of the great five tournament. So if you call a monster weak than you are calling yourself weak because you simply cant train it right.

~Redkat22~

No, I train those monsters the exact same way I trained all my best monsters. I even give them the same treatment and everything, but they just can't fight as well. I raise their parameters as much as I do with others (if they actually pass the trainging), but no matter how much I train them they still can't fight. Their attacks aren't that great, anyway.