It's true that Cubase SX 3 and below have poorer performance on Macs than Mac optimized programs like Logic and DP but the new Cubase 4 is Universal Binary and utilizes multi-processor support etc and is optimized a lot better for Intel Macs. It might not be as efficient as Logic, seeing as Apple own Logic and only want Logic to be used (Garageband excepted).
For windows this is a good comparison...
http://www.digitalmusicdoctor.com/shoot ... ummary.htm
Note the poor features and performance of PT. Now I am not comparing this against a PT HD pro studio setup on TDM but LE and M-Powered not only look old hat, they are just blah. This is coming from a Cubase SX3 user - yup, Steinberg don't design interesting products either but heck, digi haven't done a whole lot with PT for 8 years, except bundle a couple of new plugins and change dull grey to slightly less dark dull grey. The best thing you can say about PT is it handles audio well and your tracks can be imported into PT HD. MIDI totally blows on it for anything except a very basic record and edit, uses stupid rtas format plugins which are not widely supported hence cost more, ties you to specific hardware, which isn't even that great, etc, etc.
Live is where the fun is at and can do a lot but I accept the limitations as mentioned by the Logic fans. Rewire can be your God. But seriously, Live can do a lot more a lot better than people credit it with. Although it's Arrangement view is not as flexible and functional as some other DAWS, it's the Session view which makes it tick...