Babolat VS Touch BT7 16G Natural Gut Half Set
Of all the brands and variations of gut strings, Babolat's VS Touch remains the prime choice and when strung right, the feel of VS gut is so soft. The degree of power and control it offers is so addictive that you'll want more but the only drawback is the price. It's routinely over $40 per packet and that's before you pay a stringer to fix up your racket. Babalot advertises a new BT7 technology added to the string they state adds 15 percent to its durability, so that might keep you away from the stringer for one more session.
If you have a fast swing then you'll want to consider hybridizing the gut with a polyester such as Luxilon Big Banger Alu Power to get a compromise of playability and power. There are certainly other brands of gut strings to consider, such as Klip and Pacific. I've played with them as well and while cheaper than VS, they’re not quite as nice. Wilson gut, Roger Federer's choice, also deserves a try but it's more expensive.