I usually just text my friends/family. But for online friends and RP, I actually have a Skype for that.
The only group chat I've really got is with my classmates and another with my group members for a project, and we use GroupMe.
Personally I don't really have any strong feelings about any of them but I do slightly prefer Skype in that I can use it from my phone or my computer. I have a Swype keyboard on my phone and always use that to write, so I end up with very bizarre typos if I'm not careful, and I kind of prefer using my computer when possible. But the mobility of having it on my phone is obviously a big priority too.