My ideal aircraft (for touring at any rate)
A DA42 with the cabin of a Cirrus, the speed of a Mooney and the engine out performance of an Aztruk. (and a bit of TB20 thrown in for good measure)
Diesel engines would be great because of the widespread availability of Avtur but Lycomings will do. For a modern twin I would want a honest cruise of 180 KT, and I think the 42 needs a little better single engine performance (its fine in the cruise but underpowered on the climb out).
I reckon the Lycoming powered version from what I have heard comes very close. Whilst I liked the laid back seating in the 42 initially I am now not so sure. The Cirrus cabin is better as is the TB20.