Not trying to stop a sale, just giving my general opinion:
LED bulbs generally give a "whiter" light, and perhaps most importantly, draw less juice that other types of bulbs (the batteries last longer). Most LED dive lights (excluding can lights used for cave/technical diving) will dim very gradually over time (as the batteries run out). This offers a tiny bit of extra safety as you won't be left without useful light like what happens to other types of bulbs, whose brightness drops very quickly at the end of the battery's life.
Batteries are an important consideration. Regular alkaline batteries leak over time, and can destroy the innards of any electric device. They also won't last as long, as say a more expensive lithium battery. I generally prefer lithium batteries, because I can drop them in a light and forget them.
I hate twist on/off light heads. While they are generally a little easier to turn on/off, it requires two hands to do so. My biggest gripe is that crud gets into the o-rings and threads of the light, and it takes extra effort and vigilance to keep them operating, and watertight. Some folks prefer twist on lights though, YMMV.
Magnetic switches are theoretically the best, as they don't pierce the housing of the body. I've seen mixed results with magnetic switches though. The ones that are the most reliable are difficult to turn on/off with a single, gloved hand, and the ones that are easily operated, tend to suffer from reliability issues (at least in my experience)