[Nerull]

Barbarians are just as good as paladins and (non-archer) rangers with bows. They can put the same two slots they can and get the same THACO. And with BGT installed, when you go to the inventory screen it pauses (i.e. uses the BG2 engine), so if you have to melee just go to inventory and switch your weapons. I would argue for bows just because of the extra attack each round. And you can honestly outrun many of the creatures in the game, so a "run and shoot" mentality works great through much of BG1. If you were using true BG1 engine (i.e. going to inventory unpaused the game), then yes, sling and shield would be good. I thrashed a good portion of the game soloing a berserker (one slot in missile weapons) using the run and shoot method with bows. And since you are playing at Insane difficulty, I would highly recommend staying at a distance.