There are many types and grades for each application. So, to say one Grease fits all is not the correct philosophy. Start by looking at what you will be lubricating, and your budget. Heavy earthmoving equipment for example, performs best with a grease that is high in moly additive content. We use a 5% moly grease that meets Caterpillar specifications(Mobil, or DA lubricants). For chassis applications, moly isn't necessary, but is ok. I like Valvoline ceroline for chassis applications. So, look at what you are doing first. Look at what grease is suitable for the application. As far as compatibility, lubricant manufacturers RECOMMEND cleaning all residue of grease when switching types. Some aren't compatible. When I try different kinds, I just try to flush out the old stuff. My personal favorite grease in terms of tackiness is chemsearch aluminum complex red. I can't seem to find it anywhere though. So, yes it does matter what type of grease is in your guns.