I have two.
Mech Bunny because it is flexible and Konrad offers amazing support and can whip up any feature you want without raping you on price. Plus it is un-encoded and has an unlimited domain license. It's not cheap but I've never heard of a single unhappy customer...the premium price is very easily justified for the scripts flexibility and Konrad's support.
Tube Ace because it is a cheap and is perfect for if you want a simple tube without a bunch of custom mods. The latest version is un-encoded and it now also comes with an unlimited domain license. I've had to reach out Chris a few times and he's always been there ... thought I had a problem once with an unanswered email but I hit him up on ICQ and he resolved it right then and there so I'm not holding that against him but felt I should mention it in case anyone reminds me of a recent thread where I mentioned that email.