Cubase - better midi and automation editing. Very good external instrument and hardware fx integration. Precompensation handling seems alot better as well. Live is just not happy balancing up multi -pre-compensated audio paths. Cubase also has very good drum mapping, and you can create youw own instrument control panels, define you own automation maps etc.
For working on music with alot of parts, again cubase scores much better - for example it has groupos tracks for creatng submixes, folder tracks for groping parts visually. For example, Ill often use folder tracks to hide all th tracks containing midi so that I dont need to see them once I have bounced to audio.
The mixer in cubase is good - has all the normal mixer type functions - rather than just levels. Out of box plugins with Cubase 4 are actually quite decent as well. I thought the ones that shipped with SX3 were more or less unusueable, but those with V4 actually seems quite decent.
Where cubase is cripppled is in it audio routing and this is where Live scores very well and for electronic music production with complex effects routings that can make all the difference.
While live doesnt directly support sub mixes, external instruments, external effects and stuff like that, its audio routing flexibility actually makes setting up this kind of behavior very easy. And because you can save parts of your set with routings and plugins intact, then you can effectively save external instrument setups, for example I have preset track collections consisting of pre-compensated MIDI tracks with an audio routing track for each of my hardware synths. So If Im using my v-synth, Ill just drag in the v-synth track collection and thats everying I need to have audio routed by from the v-synth directly back into live - Ive actually mixed down from a bunch of hardware synths without bouncing the midi to audio first. Probably in the end - Live is more flexible in how it can handle external hardware and bring it into your sets, rather than just dumbly sequence them.
Personally I use two DAWs - Live for the creative part, Cubase for the post production part. Thats mainly because Cubase works alot better with the high pre-comp values required when working with DSP card hosted plugins - powercore, UAD etc.
They both have copy protection issues - Live just random out of the blue, Cubase - that can sometimes get upset around driver updates. One annoyance with the Cubase dongle - its such a cheep nasty bit of plastic - considering that as far as steinberg are concerned, the entire value of the product is linked to that dongle - they could at least make them a bit more solid.