For just about the same reasons you stated (new acoustic, new artists, no time to set up, no chance to move the mics during the performance, not sure how much "room" the artist wants in the recording) I often use a Double MS setup. Like the "regular" MS, the DMS has a side facing figure-8 for the Side signal, but the Mid signal consists of a Front and Back cardioid mic. So by recording three channels, Front, Back, and Side, you can have a front pair of virtual mics with any pattern separated by any angle. It is also possible to derive 5 channels of surround information from these three mics.
For a recording mixed to two channels, in simple terms the image width is adjusted by the Mid/Side balance, and the ambiance is adjusted by the Front/Back balance. When I use the DMS I tend to place it a bit closer to the performers than I would a MS or ORTF rig because the Back mic allows me to add lots of reverberation if I want. Like I tell my clients, it's easy to add chaos, but removing it is difficult. Since DMS is coincident, there is never any phase issues when mixing the signals.
As for my specific rig, I most often use a Sennheiser MKH-800 for the Side mic, and a Sennheiser MKH-800 Twin for the Front and Back channels. Thus with 2 mics I can get the three channels I need, which makes for a compact setup for the live concerts often record, and the Sennheisers are very fine mics. I've used other mics in a DMS configuration with fine results also. I use DMS so much I've built a 3 channel snake, which it's just a 7 conductor mic cable with the appropriate connectors on each end. This really speeds up and cleans up my setup. My recorder is a Sound Devices 788T, and I use its internal pre-amps which I have found to be more than adequate.