Android IM apps: which one should you use?

I'm a big fan of instant messaging apps. They're fun and easy plus, like Google Voice, they're sometimes a money-saving alternative to texting via your mobile number. Living on the west coast, they're one way I keep in touch with my east coast family, especially my busy brother and my mom, who loves her iPad's expandable, easy-on-the-eyes fonts. Plus, I sometimes ping Ars' staff on their IM