I find the strategic game a lot harder than the tactical, at least if you want to keep every country. So I always go for boosts to the strategic game first.

Also, I've found that if you rush Firestorms and EMPs, they're the only improvement you need to your interceptors. You can go straight for them, and skip Phoenix Cannons, Laser Cannons, and Plasma Cannons. That's a lot of time and money saved that I prefer to spend on other things.

So my research order is pretty much always UFO Flight Computer first (gets me satellite nexus), then UFO Power Source, then Firestorms, then EMP. For primary research. In between I'll grab some short time research options, but most of my time is spent in that order.

Since the EMP is one of the two max damage weapons in the game for interceptors, and its more accurate than the Fusion Lance, I pretty much use it as my only weapon once I start getting the higher level ship classes. It also keeps every piece of gear on the enemy ship intact, which means I can get more research and more bonuses back quicker.