I use Bimectin which is the safest on the market thank goodness as per my vet. I used one at christmas that had a defective plunger and gave the entire tube to my litte 200 lb mini by accident. I have never been so scared in my whole life as I thought the worst was going to happen, my vet managed to calm me down and told me that I was very lucky and that all Mouse would get would be poopy bum which did happen.
Bimectin is merely Ivermectin under a brand name. It is safer than Moxidectin by far, and my wormer of choice, but it's overdose rate is much much lower than Fenbendazole, which actually is the safest (but also, therefore, not nearly as effective).
I would never pay more for a brand name than I would for a generic Ivermectin product- they are all exactly the same. So long as they contain 18.75% Ivermectin you are good to go!