Are you talking about Jean Auel's "Clan of the Cave Bear", "Valley of the Horses" and the other books from the Earth's Children series? If so I'll have to agree with Joshua that they are really hard to compare because they are almost two different genres.
I enjoyed Martin's books better because I feel they have a better focus and more realistic characters. After Clan of the Cave Bear Auel's characters just seem to drift around and and plop themselves into situations. The only real focus seems to be exploration and soft porn. The plot often seems less important than character interaction (not character developement since her characters don't seem very dynamic). Furthermore, Ayla was just too much of a superwoman with discovering flint & stone make sparks, inventing the bone needle, inventing spear throwers, taming lions & horses before anyone else, and being the uber-healer/priestess. Frankly I got somewhat bored reading how great she is and how wonderful sex with her is. After the first book, each other one went progressively downhill for me to the point where I haven't bothered to get/read the last "Shelters of Stone." If it's anything like the previous two books, I can guess the plot: Alya tries to find acceptance by sleeping with Jondolar and maybe a few others while showing off her wonderful inventions and curing people that no one else can.
Martin on the other hand has continued to impress me and each book of his I find better than the last.