The most versatile ROD you use for aluminum TIG welding is the 4043 aluminum tig rod, the versatility of this rod is really amazing which is versatile for 6061, 3003, a355 aluminum casting, etc.
As for other use, you also get some 4047 rods for casting where porosity is rare; 4047 contains almost 12% of silicon, which makes the flow better and crack less.