I might be a bit off on this as it's been a couple of years, but IIRC, both FRS and MURS require certified radios. FRS is limited to like 500mW effective radiated power (ERP) and MURS is limited to 2W (not sure if that is ERP or conducted? I think it was conducted).
GMRS is limited to 15W ERP for base station and 50W ERP for mobiles, and requires a license.
Like said, it is easier to determine the right tool once the specific task is defined. Or we can talk about specific tools and how they perform.
I think the better GMRS/FRS hybrid radios have come a long way from the FRS radios of past, but like mentioned, they are still 4 or 5W models with limited range. Still a 5 mile radio if you are lucky, really lucky. But close range communications or nice with the advanced tone encode/decodeing, etc...and it is FM quality voice. Very good for their intended purpose.