Horde beacons have been nerfed in how they give out loot due to their new scaling which uses Square-root so 4 players would be Square-root of 4 which is 2X the original loot(which is 8 btw)
Using my school calculator i decided to make a nice comparison graph on difficulty vs reward
The intersect point of this is 1.So if you wanna get the best difficulty/loot ratio Just do it by yourself.But(this is my opinion btw) If you wanna squeeze as much loot as possible while not sacrificing too much difficulty. I would say bring a 3 or 4 player squad and hope for the best.