Best strating monster in Monster Rancher advance 2?

Truthfully, there is no "best" when it comes to the MR franchise, as there are many different types with totally different fighting styles.

When I first started playing MRA2, I regenerated a full-blooded "Antlan" and began to train it. I've found that these type and "tiger" types are easy to handle and, with a high enough POWER stat, can knock out ANY monster with just a few "fire punch"es or "scratch"es. After you get you POW and DEF up to 500+ and 400+ respectively, you shouldn't have trouble with anything all the way up to S level tournaments.

Also, CHOOSE COACHES WISELY! They make all the difference!