As a bluegrass fiddle player, D'Addario Helicore are my strings of choice. If you play all styles of music, including classical, alternative styles, folk and bluegrass, these strings are for you. They are very versatile with quick bow response and short break-in time. They tend to stay in tune, even when played very aggressively and can withstand a variety of climate conditions as well. I change them once every 3-4 weeks in the summer season, which is pretty great, considering how often I play.  I use heavy gauge because they provide a fuller sound and work better for the style of music I play. They feel soft under my fingers, flexible, but not flabby.  The E is particularly soft feeling.  

As a steel core string, it is made with smaller diameters, which improve bowing response. When combined with D’Addario’s dampening technology, these strings can be played with very quick and easy bow response. The flexibility of stranded steel cores adds greater sound complexity, producing a clear, focused and dense tone.  They aren’t too bright, and really improve the tonal quality of a dark sounding violin.  I highly recommend these strings to students and professionals alike. ~ Beth Kelley  

Here is the link to where you can buy them