I've owned Logic 6 and SX for Mac. I prefer working with Logic, despite having been a Cubase user for 10 years. It probably took me a year of average hobby use to get competent in Logic, but I feel it was worth it.
The only thing I miss is the Phrase Synth from Cubase..

Since SX2 has just been announced it might be a good idea to wait and see how the features compare.