[@Kazemitsu]
Slimes will be somewhat similar to their Dragon Quest incarnations, with options to simply increase their size or defense, but because Slimes can be found in some form pretty much anywhere and they can eat/absorb pretty much anything, some of their options will be heavily dependent on their environment. We'll be starting in a typical sort of Noob Cave, but by traveling the world of the RP you could find many other terrains to influence your character's development.

Lizards will be a good choice for the crafy, strategic player. While they're similarly weak in up-front encounters as the Magic monsters, their status effects can work even on higher level monsters. They don't have as many Transformations to choose from at the first rank as some of the other starters, but the ones they do have all seemed (to me anyway) to be very reliable.

[@Gobby]
Dire Rats are, along with the Goblin, probably a good "standard" choice. Magical spells take time to learn, even for monsters with those natural abilities. Their eventual payoff is worth it, but if you're looking for fighting ability right at the get go the Dire Rat's got that. Plus, while it's somewhat limited at first, any monster can eventually learn magic or transform into a magic-focused creature later on.