Ready mixed filler products are easy to use and especially useful for small quick repairs. This is because, unlike powdered fillers, most ready to use products can be used in small quantities straight from the packaging. They can also be stored for later, with no wastage.
Once dry most ready to use fillers are much stronger than powdered products, this makes them ideal for creating long lasting repairs. However this can sometimes mean that they're harder to sand. Additionally ready mixed fillers are particularly ideal for infrequent repairs to things like screw holes and infrequent imperfections. Especially when only a small amount of filler is required. Although they can sometimes take longer to dry than powder filler.
Choosing the best filler for the job mostly depends on location, material and the type of finish you desire. Are you filling inside or outside? Will the material be subject to movement or expansion? Like, for example, gaps around a door frame. After narrowing your search consider the finish, are you going to paint it? Finally contemplate speed. If a quick drying time is important a light weight or two part filler might be a good choice. Alternatively using a high performance powder filler might offer a better solution.