I can't disagree with Geo. DOT 5 has many good qualities (won't absorb water, rated for much higher temratures, won't lift paint) but to use DOT5 you need to completely flush the system of DOT 3-or-4. as the silicone is not compatible with the mineral based fluids.
SO if you're just looking to maintain your current system, unchanged, your best bet is DOT 4. most commonly found in the form of Castrol GT LMA (lma stands for low moisture absorbsion).
Otherwise, there's nothing wrong with checking out DOT 5 if you're intrested in converting.