Overall probably the various Cessna Citation SP models.

Best as IFR airplane for me personally means safest.

As far as single engine goes, the Cessna Caravan comes to mind. For
pistons:

TURBO SKYLANE
- very stable
- enough power (turbo) to get out of/over all kind of weather
- very forgiving over-weight and wing contamination (ice)
- slow, which in some ways is safer
- to my knowledge there has never been an in-flight break-up
- landing and take-off possible at pretty much every airport in
existence

Gerd
T182 C-FDOW

PS: Just to pre-empty some of the comments to come; yes, I know it's
a truck but that's the way I like it.