There are primarily two filler rods used for the most common structural aluminum (606x-T6 series): 4043 and 5356.
5356 provides for higher strength Ftyw = 15 ksi
4043 is a little lower at Ftyw = 11 ksi
The allowable (ASD) values are much lower than the Ftyw values, and can be found using ADM.
Use 1/2 of the base material strength when designing welds in aluminum structures. I don't think the electrodes matter that much. What happens is that during the welding process the aluminum looses it's "tempering" and there is a significant change in properties.