I beat the game for the first ending and I have gotten all of the paradox endings as well. I'm working now on getting all 160 of the fragments so that I can get the hidden ending. Currently at 69% of the trophies.
I guess you could say that I really love this game. A lot. More than I thought I would.
If you're still playing, I can give you some monster recommendations. FWIW, none of the nine unique monsters are really important as far as that goes.
COM: Dragoon (found in Augusta Tower). Use monster materials that give HP so that it has high HP, and infuse health bonuses.
RAV: Cloudburst (found in the Archelyte Steppe in cloudy weather). The Cloudburst has a really useful Feral Ability.
SEN: Bunkerbeast (Yassif Maschas). It's slow to grow but apparently can have upwards of 1K HP. It doesn't learn Mediguard so you'll need to infuse it with a sentinel monster that does.
MED: Flanitor (Augusta Tower). Has a very useful Feral Ability as well. It could probably use more HP, though.
To be honest these monsters got me through most of the game after I caught them, and through the postgame bosses as well. The only monster I've encountered that I haven't beat yet is Yomi. Even with my characters roles all maxed out at level 99. It requires a very specific set of monsters and paradigms, it seems.
Noel makes the best commando, really, but if you have paradigms that require more than one COM or you need Noel for another role, then the Dragoon is pretty awesome.
If you get the DLC and you get Lightning, she's a grade 5 Ravager "monster" with a max level of 13. But she comes knowing a lot of useful skills already, and her Feral Link ability is Army of One. You can infuse her with other skills, too.
I'm excited for more DLC with the game. The next one is supposed to be about Sazh. And possibly include Jihl in the Coliseum? I wonder if she would be a SAB monster. :lol