When I plug my bullets from my SMC rf-120 into a 2s the bullets spark at the connection. This does not occur with my rf-170. What should I do? Is it ok for the batteries?

Probably okay. I've even seen my Deans spark at times on some batteries, some cars. I don't know why some do some don't but I've not had an issue with pre-mature wear on the ESC or battery (or charger for that matter) on those batteries that spark. Maybe has to do with static build up, not sure.

I would inspect the connectors periodically to clean and remove any burn marks as it can increase resistance.

this happens to me with some speed controls and not others. a little off-putting but I've never had an issue.

Very common, and nothing to worry about. You'll also notice that if you unplug the battery and then plug it back in it doesn't spark the second time. My understanding is that the initial spark has to do with the stored energy in caps on the ESC. One of our electronics gurus would have to confirm that though.

Ok thanks for the responses