Hmm, both are pretty similar right now, but there are a few distinct differences.
Firstly, the gun bourg has higher attack power (just 5%, but it is there) base, but the artisan has 10% more defense pierce (with getting the unique passives, it's 45% on bourgs, and 55% on artis). I think that cause of the 10% defense pierce, artisans would hit more damage than their bourg counterparts when it comes to basic attacks, but I believe bourgs had higher skill powers on their second class skills and do more skill damage.
In regards to skills, there's two skills I should mention here: The bourgs zulie stun and the artis hypno shot.
The hypno shot is a skill that is incredibly useful for pvp, but perhaps not so much for pvm king farming. The zulie stun on the other hand is less effective in pvp than the hypno shot, but it can help with things like king farming.
But one of the major differences is that the artisan can get the judgment knight summon, whereas a bourg has to make do with two mercenary hunters. The judgment knight is by far one of the must have skills for a battle artisan, and it is the main reason why people play battle artis instead of bourgs. Although the bourgs have an aspd buff and reflect aura, it pales to what the judgment knight gives (besides, reflect aura is only really useful when you can take a good deal of damage, which a dealer can't, and the aspd buff is 15 seconds).
Normally I'd say, go for battle artisan, but you're saying you also want to use that character for king farming. In terms of damage, I do think the artisan would outclass the bourg, but for farming (especially king farming), it's nice to have that extra drop chance on stockpile.
In terms of gear, I'd go with a courage set for pvm, for the high amount of pvm offense. I suppose you'll use a cleric to support your character, so it'd be fairly easy to keep yourself alive, even when fighting kings, so you should just purely build towards dealing damage, for which the courage set would work best. In terms of accessories, a hebarn set isn't bad, for the attack power and crit (you won't need a lot of accuracy anyway, so lava set is a no go), and I suppose a hiria's tear would be good (the 40 con gives a lot of attack power, more so than a piece of hebarn in fact). I'm not all too sure in terms of what gems to put in there, or use a specific stat (like 25/50), so I'll leave that one out.
For pvp, It'd probably be best to use a chiva set. People tend to pack up, so moving about isn't usually necessary, making precious not that wanted at the moment. Luminous is well.. luminous lol, out of the question. Glorious, although giving 30% aspd, doesn't really cut it against the attack power which chiva gives. I'm not an expert on this, so I suggest you get both glorious and chivalrous, they both seem to be viable sets.
For masks, I think either an ashura mask or star glasses would be fine. You don't have a lot of buffs/debuffs so there's not much use for charm (if you do use a bourg, you may want to use style sunglasses). Substat on it should be 25/50 or 12con 20ap.