If you just want to resize, crop or do some basic retouching then just use your Iphoto on the Mac. If you want to do some fairly cool advanced retouching etc then you can't beat Photoshop.
I store all my photos in the Iphoto program and back them up on CD.
Photobucket is a good site, but I always re-size before uploading it is just easier.
All the best.
Mike