I've auditioned both these pre-amps in home each for several days. The Line 3 is very neutral musically, whereas the SFL2 is more rich, a bit warmer, more "tubey", and IMO is the best sounding pre-amp SF has made. But, the Line 3 has many more features such as an excellent remote control and headphone section, and has finer volume control.
Thus far I have chosen to stay with my Line 2 though as it has all the features of the Line 3 and is also very neutral. The Line 3 as noted above does have a really beefy power supply, ie twice as big as the Line 2s. If possible, you should audition both these fine pre-amps. BTW, the Line 2 is a different (newer) pre-amp than the SFL2-- the model numbers can be confusing. Good Hunting. Craig.