I only play as rangers and only as RAcaseal at the moment. I like their endgame abilities and benefits. Get to see traps, use traps to restrain powerful enemies, immune to most adverse effects that can always be annoying no matter what level you are, instant healing with mates which is what pretty much all classes end up using often in endgame, good armor so you need less support from your party, access to things like Iron Faust, and so on. Otherwise I'd be a RAmar like I have since Dreamcast. I pick rangers because I love their play style and equips. I think RAmar is probably the best starting character. It's a pretty balanced character. Good ata to use new weapons quickly, resta to help with getting beat down, easy to use exp hoarding weapons, and overall access to some of the best gear in the game for kicking butt. I hear RAmarls are good for soloing, RAcasts good for ATP, and RAcaseals for heavy defense.
For IDs I usually use White or Blue as they have some good ubers in areas I like to play in.