The E2DL Ultra came out before the EB2. In fact, it came out before most of us knew that the EB2 would even exist. When the EB2 came out, it was basically "like the E2DLU, but with some differences," so it did not make as big of a splash.
Those differences are:
- E2DL is shorter
- E2DL has spiky crenellations
- EB2 is longer
- EB2 can be clicky (pro/outdoorsman style) or 2-stage twisty (tactical/aviator style)
- EB2 is sleek, E2DL is knurled
To me there's not that big of a difference unless you want the twisty EB2. The clicky version is nearly identical. If you wear slacks, the EB2 will have the edge, as the lack of knurling and crenellations will not tear up pants. If you want something a little more defense-oriented get the E2DLU.
I have the E2DLU. I chose it because I could get it cheaper. To me, the small differences do not matter one way or another -- both are Surefires, both have the same lens and same regulator, and either would suit my needs.