Zap a Gap, there's a bottle permanently on my fly tying bench and one in my base camp bag when I go fishing all the time!.I use the one with the little brush.
I find it invaluable and have used it for years, waterproof and with a degree of flexibility.
Wouldn't be without mine!
I'm another for the Aquasure - flexible and a good hold but use it in conjunction with the rubber sleeve that comes with the leader loop. Also check it a few times through the season with a good tug. I hadn't checked mine for a bit and one light pull and it came away easily- you dont want that happening on your record fish! Lesson learned....