Hyperfirm will be likely be the lightest but they are not very accurate. Passable for sure, but if your looking for as accurate as you can get, stormrider, sidewinder, or MLS are the way to go.
I dont have one of Stormriders rubber EE-3's....yet,...lol... but i think they will be the best out there when it comes to accuracy in a rubber based blaster. I dont know how the weight would compare to hyperfirm though as they have some proprietary rubber/foam, supposedly, but i think Stormriders will be a great choice if he does more rubber ones.
Generally speaking i think Stormrider Sidewinder and MLS have comparable blasters. They all use real guns as the base. So the differences are very little visually. I think the barrel mounts are the biggest differences between them all, and even that isnt much.