Depends what framework you are using, but I can provide some insight from experience with Buffy and some other things...
The most popular LCDs used are the same physical LCD panel used in Color DMD sized at 15.4", with a resolution of 1920x1080 --the common usable aspect ratio based on the speaker panel cut (visible space) is 2
--a standard dmd cutout is 4, so just route the opening to be twice the height my increasing by about half the height above and below.
Your resolution depends on the framework. In the case of SkeletonGame/PyProcGameHD the limiting factor tends to be the gpu and available VRAM. People use it scaled up using hardware pixel doubling (eg, Buffy runs at 450x225 with a 4x scaler), I believe Eric said ironman HD runs at full HD. You find lots of options in between. Doom is running half of 1920x1080 (running at 2x scale). I don't recall what resolution Josh is running on Casino but it might be the same as doom.
If you don't want a standard sized head/translite, Scott's Total Annihilation is running the full sized panel, as is Nightmare before Christmas.
I have a post on the pinballcontrollers forum which documents my media tools and workflow but that's old and I'll bet what Eric is doing with Ironman HD might be smarter 
