The fact you have a Mac is irrelevant as the same software for photo editing tends to be available for Mac and PC. The main exception being Apple's own Aperture.
It is not like other software (i.e. games, product stuff etc,.) that is never made for Mac and is a bit frustrating but them it is a much smaller market.
Mac's tend to be used by "visual" people so you will find most things are available in that field.
I have tried Lightroom, PSE 8 and Aperture and for ease of use I liked Aperture as it is more Appley (but I have used Apple for over 10 years so may explain that!)
I do however feel that Lightroom does more though so if I had just come from Windows and was used to having to use unintuitive software I would pick Lightroom
What software did you like on Windows?