Managed to hunt with a group of HR70's yesterday, and nabbed myself a ton of rathalos items. I've been thinking of adding a bow, but can't decide between a rarity-4 with 140 power/1 slot/200 water damage or a rarity-3 with 160power/2 slots/200 explosive damage.
You should really ignore rarity, it's basically meaningless. As for your choice, Blast damage got a huge nerf this generation and is next to useless unless all 4 hunters are using Blast weapons, which is unlikely. Coupled with the fact that nothing is weak to Blast, you'd be better served with an actual element.