To Quit of Not to Quit, That is the Question

     Ok. I'm about to admit it. Here it comes. Cue the face-scrunching...

     I'm thinking about giving up.

     Well, ok, not really. I'm not going to give up writing- no way! And I'm not giving up querying Daze and Knights... yet (although I'm on a temporary hiatus while I wait for a query critique).
     What I'm thinking of giving up is the sequel to Daze and Knights- as yet untitled. Here's the thing. I'm almost done. I know I can push through to get it finished. So why quit? Well, I have the ending planned out. I know what I want to happen. But while doing my research I've realized that I have a couple of weeks before this event can take place. So I had an idea to put Jessica right into the war, but that means a lot more research and a lot more writing- more to the story than I had planned in the first place. A part of me wonders, why bother? Because if Daze and Knights never goes anywhere then it doesn't really matter if I get the ending written. But then my controlling obsessive side argues that I can't leave it unfinished.
      Here's the other problem: I've got a completely different story idea stirring in the back of my head, just waiting for me to get it started. I'm practically itching to start writing it. It would be so much easier for me to quit the hard research/ending writing, to start something brand new.
     So what do I do? Take the easy route? Quit what I've almost finished and start something that I could actually query when it's done? Or should I take the harder, less-rewarding route. Finish Jessica book 2 just for the fact of finishing it, even though I won't be able to do anything at all with it?
     Any advice?