A compact cardioid microphone directly on a viola
Point DPA 4011C compact cardioid microphone directly at an area of the instrument and thereby enhance a special sound, i.e. timbre, bow sounds or finger sounds.
Furthermore, the 4011C is under influence of the proximity effect, which can be used to enhance the low frequencies of the instrument and thereby give the recording more body.
This set-up is also excellent for live sound applications.
A miniature microphone directly on a viola
For live use (or home studio) the d:vote™ 4099V clip mic may well be the ideal solution. The 4099V has a supercardioid polar 
pattern that allows the mic to focus on the instrument and get a good isolation from the other sound sources on the stage or bad acoustics.
This also reduces the risk of feedback significantly, while keeping the rich and nuanced sound of the instrument uncolored.
However, because of its high directionality some time should be spend on finding the right placement of the mic. The position will always be a compromise trying to capture the whole instrument with a narrow pick up pattern. The clip (VC4099) included with the 4099V offers a unique solution that is both secure, highly flexible (fits also violin, mandolin & banjo) and very gentle to the instrument.
An even smaller and yet superbly sounding microphone is the miniature 4060 omnidirectional microphone.