The best tires in that size (245/40-19, same as BMW 5-series M-Sport) are:
Summer: Michelin Pilot Super Sport (introduced 2011), Y-rated, 300 wear rating
Winter: Michelin Pilot Alpine PA4 (introduced 2012), V-rated, no wear rating
All-Season: Michelin Pilot Sport A/S3 (introduced 2013), V-rated, 500 wear rating
There are less expensive Conti (ContiExtremeContact DW and DWS) and Bridgestone tires that are less expensive and good, but not as good as the Michelins.
If you must have a runflat, the Bridgestone RE960AS Pole Position RFT is probably best (wear rating 400, introduced 2011), but the newer RE970AS was introduced before the RE960AS in an RFT.
Since the Q50 has a spare available, the non-RFT is not an issue. An inflation kit, such as the ContiComfortKit ($79) are also available.