Nothing will cause more muscle tension and shot anticipation than a cheap release aid with a lot of trigger travel. A really bad trigger can actually predispose you to target panic. So, if you can afford it, I would encourage you to buy the best release aid you can find.
I use Carter release aids for a lot of reasons, but the main reason is their incredibly crisp triggers. However, a lot of other release aids on the market have good triggers as well. If you can, shoot a bunch of different releases until you find one with a really smooth trigger. You should not feel any trigger movement before the shot.
It doesn't matter whether the trigger has a light pull or a heavy pull. Either way, the trigger should not move until the shot goes off, period. If you can feel the trigger moving, release of the string is not going to be a surprise because, as you get closer and closer to the point of string release, you're going to feel more and more anticipation, which only makes you more likely to punch the trigger -- with nothing but bad results.