This really is a tough decision, given that we really don’t know how Jingle bell, Jingle BAM is going to be, though I’m sure it will be wonderful. I agree with @bswan26, if you’ve never seen F! before it really is a must-do attraction. Advantages are that it has seating, and I also would recommend the Fantasmic! Dining Package, and if your DS is into characters, the one at Hollywood and Vine might be a good option, as they have Disney Junior Characters at lunch and the fab 5 at dinner (Mickey, Minny, Donald, Goofy, and Pluto, I believe). It is a little on the expensive side, but I agree it is worth the expense for the view at F! and the time you save by knowing you have a reserved seat - also, if you’re doing the Disney Dining Plan, you can use a table-service credit for it, which make it more affordable.
I will admit, on my next trip, I’m going to be skipping F! in favor of the Star Wars dessert party, but then I’m a huge Star Wars fan. I’ve also seen the DL version of F!, and was disappointed in the WDW version after seeing the DL show. That being said, I loved the WDW version the first 2 times I saw it, which was prior to experiencing the DL version.
Good luck making your decision - I know the pain of not having enough nights at WDW to experience each of the night-time spectaculars/fireworks.