Well, both platforms require you to use a new currency (ether and XCP currency.) Counterparty will make it easier to write contracts that involve bitcoins (I think, not totally sure how that works) ethereum will have a 12 second block time vs a 10 minute block time (very different) and ethereum transaction costs should be lower (for several reasons.)
Additionally, counterparty will probably launch their product first.
Also, ethereum is only one piece of a much larger technology stack being worked on, linking contracts to things like private messages between users, a file distribution system, a webkit-based webrowser/wallet system, etc. Additionally, ethereum can support SPV, a technology very relevant for mobile apps, which apparently isn't possible with a XCP-type system.
(Counterparty also has add-on technologies, but I'm not that familiar with their stack.)
So it's confusing, but Counterparty doesn't exactly require new currency. There's a few ways to think of Counterparty's XCP, but in all of those ways it augments Bitcoin. XCP is used to store 'value in escrow', fight spam (such as in the case of asset name declarations), and now to control of execution times. There may be some other uses in there.
The 12 second blocktimes of Ethereum will be considerably longer than the instantaneous times of Bip70 insured (or let's see what medici comes up with maybe) Bitcoin/Counterparty transaction times. Further the chain will almost certainly be less secure, but since this chain doesn't exist even in theory yet, it's hard to say.
As for the rest of Ethereum's promises, yep, they're tackling just about everything that could ever be included in a protocol. As to whether any of this will scale down to a mobile device, it's just a marketing claim right now, they have way to much work to do in the base platform to care at all about mobile yet.
