Depends on what you expect to need it for. I've used normal strap on masks but only have limited experience with full face masks. For most normal "protective" issues I would say a half mask is fine. Don't go the cheap route and get paper ones get an actual strapped one they work much better. I think that is probably the best bet albeit a little bulky.

But when you cross over into the emergency response area I think a full face mask is the best option. I've only used them for spray on applications with a full suit so the whole thing is encumbering but for any unknowns a full mask offers more. Especially for limited body exposure. In an emergency you want to mitigate as many risks as possible and I think covering your delicate areas (especially the eyes) is the best bet. The problems with them are they are expensive, the cartridges are expensive, ALL of them fog up at some level, and they are hot/heavy. Most of which can be dealt with but you have to go a little slower and have a little restricted awareness. I would get a CBRN (chemical, biological, radiological, and nuclear) compatible one. I've only used 3M ones but they seemed to be quality. I would also highly recommend the peel off mask protectors otherwise you will muck the visor up and you can't just buy replacement visors.