I've used both and they sound really similar but the Dunlops were dead after a month and the SIT's lasted five months.
I did take the Dunlops off once to clean the bass so that might have had something to do with it, but I kept them away from the cleaner and wax by taking them off.
Dunlops have lower tension and a more midrangey sound. They are very similar to DR Sunbeams. You also don't have to worry about buying 'long scale' or 'short scale' with Dunlop, they fit most anything.
I actually like both strings. You can't beat SIT for the price, but I mainly use Dunlops now. I just like the sound and feel better.