Well it depends a lot on what you want to have ultimately, how much you're willing to spend, and how much modding you want to do yourself.
Incandescent choices with a 2D are kind of limited to the Roar of the Pelican modification. There are plenty of threads on how to do this but expect to invest a reasonable amount in battery holders, batteries (if you don't have a bunch of AA rechargeables lying around), reflector, lens and of course bulbs. I'm sure a budget is posted somewhere, but as I understand it unlike a Mag85 the mods are pretty straightforward.
LED choices abound really and it is a matter of what you want (huge output, long runtime, etc...), how much you want to spend and how much work you want to put into it.
Due to ease and relatively low cost I upgraded two 3D Mags with MagLED bulbs I bought used in the marketplace or on closeout. I upgraded one 2D with a MagLED and another with a Niteize LED drop in. All can use alkalines, the MagLEDs put out a decent beam and run for quite some time so they are useful lights and great emergency backup lights as they can be used in candle mode. The Niteize drop in runs for days and days and days. Not real bright but bright enough and a great power outage light. All the other options seemed to be more money than I wanted to spend (multi die setups, etc...) and the MagLED and Niteize drop ins were sufficient to make them useful lights again without spending very much at all. I do think they are about as much bang for the buck as you can get and while not perfect, they seem to be a bit underrated...
