I didn't ride the Tiger, but I had F650GS, and now I have a Vstrom650.
For dirt roads F650 is by far a better choice, especially if you choose the Dakar version. DL650 doesn't handle well offroad, it also feels not very tough (the F650 isn't too tough either, but it's tougher than the VStrom). ABS is also a good thing about F650.
I have a DL650 now, because it's cheaper. Besides I do a lot of road touring with a passenger - the DL is bigger and has much more power, so it's better for such riding.
If you ride solo, and the 48HP is enough for you, then the BMW will suit you much better. The good thing is the fuel consumption - f650 takes about 30-40% less fuel then the DL.
Both bikes are very comfortable (the DL's windscreen only sucks) and allow fast cornering on roads. My F650 made about 35000km with no technical problems at all, the DL has 5100km so far and no problems as well (meanwhile Transalp 650 - did 45000km and again no problems). These bikes are simply very reliable.
Killer Wee (Strom) K6 => DEAD
DRZ400E '07 => alive