I think Gaga’s crazy wardrobe is more well-received because it’s seen as weird performance art (even if it is partially about attention-whoring), while Christina’s fashion was disconnected from her music and it felt like she was trying too hard to be little miss sex symbol when she was talented enough to not NEED to use sex to sell her music (unlike other blonde pop stars). 

That, and Christina started out as a teen singer who was marketed to a younger audience, and parents criticized her heavily for being a bad role model even though she never wanted to be one.  It took Christina a very long time to get people to stop expecting that of her.  Gaga’s music was never considered “teen pop”, so she was taken more seriously by the media.

I admire Christina for getting out of her comfort zone with every new album while Gaga seems to just do the same thing time and time again.  I also happen to think Christina’s music is slightly less shallow – sure she sings about sex and stupid cliche things a lot, but Gaga is very artificial while Christina has had the courage to step out and put her personal life into her music every so often.  
It’s not like Gaga was the first to come up with expressive, abstract fashion or music.  Both are talented, but it isn’t fair to call Christina a ripoff when both of them are heavily influenced by singers who came before them (like Madonna) and they have different influences as well.  People who argue about who copied who are obviously too young (or too musically illiterate) to know how far back these influences reach.