I have a 48 sniper and a 42 'slinger. Honestly, sniper is boring. 2 levels from 50, and I've shelved him. Gunslinger is a lot more fun. Here's why:
Story. Agent may have an awesome story, maybe the best, but the smuggler is so iconic, and so "piratey" it's a lot of FUN. Yes, you may not blow up thousands of people, but it sure as hell is a ride.
Animations. Sniper. Fire. Fire. Fire. Probably the most boring animations in the game. The most interesting animation
is Series of Shots, which isn't that interesting... Oh, and Shiv, but you'll hardly use it. Gunslinger may be a little repetitive, but at least you fire different, and you play more as a cowboy, ducking, firing quick shots, hiding, fighting dirty. Never gets old.
Style. The look of a smuggler is awesome. There are a lot of choices. You can go for the iconic Han Solo set, or maybe a fur coat and a "cowboy" hat, or you can gear up and go for a techy look. Civilian or Cyborg warrior, choice is yours. Plus, you get dual pistols, or you can switch to one for RP or fooling around if you'd like.
Companions. I love the smuggler companions and the ship just because they -feel- like a smuggler. Agent's companions, while great, don't have the same sense as the smuggler's. Corso is like Luke, Bowdaar Chewie, Risha Leia, and you're Han. Then you get Akaavi, who is probably one of the most BA companions in the game. And Guss, arguably the best companion in the game. Definitely feels like a rag tag team of smugglers.
Convos. Smuggler really shines on his funny little phrases and neutrality. Agents may get flirts and such just as often, smuggler really feels like they were catered for them solely.
Want the wildest adventure in the game? Smuggler probably isn't for you, although it is wild. This is more of the calm, funny story that gives you a break from saving the galaxy and killing legendary foes. Instead, you get girls, money, and, well, a Wookiee.
See you on the hyperspace lanes.