^ 2nd'd
No difference in the polar responses between them, the difference in on-axis frequency response tracks the same difference in off-axis diffuse response, making them "EQ interchangeable", meaning an carefully tailored EQ correction to one type can emulate the other type precisely.
Either can work well in your stated application, and preference prior to any eq adjustment will probably depend on how bright the direct sound from the strings and how bright the room sound is.
Regardless of which you choose, consider experimenting with the sphere attachments for this application. They can work nicely for this, and are different than switching between the various omni caps with differing frequency responses precisely because they do modify the polar pattern, varying the on-axis against the off-axis diffuse response. In other words, they change both the frequency response and the polar response. Combine that with EQ to offset on-axis response of the sphere attachment and you have a way of varying the off-axis room timbre without changing the on-axis response - or vice-versa.