There is no best - they just have different personalities.
The best sign for Pisces is Cancer, Aquarius, Scorpio, and/or Virgo
Scorpio is a water sign and would have the best connection with a Pisces or Cancer.
Taurus, Leo, Scorpio* and Pisces*.
I am guessing you want to know which signs are best for scorpio... Well, cancer rocks but pisces, taurus and capricorn can work magic too. But given the theory of earth and water great compatibility, scorpio and virgo too can be a success.
Generally speaking Cancer-Scorpio relationships are harmonious.
In Western astrology, the water signs are Cancer, Pisces, and Scorpio. These signs relate to the creatures of crab, fish and scorpion, and are emotional signs.
Cancer or Scorpio
Scorpio
The best zodiac sign for Cancer would be Scorpio, since they understand each other's emotional needs and insecurities very well, and Scorpio would not at all mind staying home with Cancer often. Pisces is also a great match for Cancer. Other signs that Cancer would be able to get along with are Taurus and Virgo. I also read in a few books and websites that Leos can be good matches with Cancer as well...sometimes xD
Leo, Libra, Virgo, Gemini, Scorpio, and Cancer.
Honestly, it doesn't matter. If you love this guy, just go for it! Don't worry about starsigns. Do you think that if you were a cancer and your mother were a Capricorn and a magazine told her that you weren't a good match she'd disown you? Of course not! She loves you!
Cancer! But scorpio, taurus and capricorn is good too. Virgo too can rock. Again all earth (taurus, capricorn, virgo) and water (scorpio, cancer, pisces) signs are compatible with each other.