Everyone has an opinion on grips, I will share mine below.

There are a few different styles of grips. Oury made their name in to motorcycle market and moved into bicycles 20+ years ago. Today their grips are largely the same rubber style, with the name OURY. They are amoungst the least comfortable grips I have ever used, however like all rubber grips they hold up well to being left outdoors in the rain   

Soft foam grips are much more comfortable than rubber, however they deform quickly if left outside in the rain. Ritchey WCS are my favorite foam grips; they are ergonomically designed and have the perfect softness. 

The biggest problem with swapping grips is the old style are hard to remove. I normally lube under the grips using a shish kabob stick and any lube that's handy. Over the years I've used grease, oil, and butter. Once you remove the old grip you can install new easy to remove style that use allen bolts to keep it attached to the bike. They are a little heavier, but super easy to swap.