By smuggler, I am think of a dashing hotshot like Han Solo. 

If you're looking for a dashing hotshot character, swashbuckler is the way to go.

Quote from 6thLyranGuard >>

If you're looking for a dashing hotshot character, swashbuckler is the way to go.

 k, but there is a catch: my character mainly uses guns.

I know, I should have specified that earlier.

Which is more important, being a Rogue, being a Smuggler, or using guns?

If you want to be a Rogue, then don't over think it. Just choose whichever subclass looks fun.

If you want to be a smuggler, then a Genie Warlock is great.

If you want to use guns, then sticking with Fighter is probably the best call.

Any rogue can be a smuggler and any rogue can use guns (although you will need a way to get proficiency).

Pick the subclass that fits your playstyle and then figure out how those features might be used by a smuggler:

• The mastermind's skill in disguise/forgery could be handy in getting goods where they're not supposed to be.
• The scout's nature/survival proficiency could be used to find the best smuggling routes through the wilderness.
• The inquisitive's skill a insight and investigation would be useful for scrutinizing business partners and anticipating betrayal.

And so on. Or you can just be a smuggler who is also a swashbuckler. Or a knowledge cleric, or a creation bard. Not every class feature needs to "prove" your backstory, you can do that solely with roleplay if you want to.

Bribery and blackmail are easier to do than a smooth line and a disguise.

I think swashbuckler works best. Just ask your DM about gaining proficiency in firearms. Pistols existed during the Golden Age of Piracy (which is kinda what the swashbuckler subclass is based on) so on a thematic level it should work.