If you say that you want to have a better loop, it sounds like you are still practising that shot.
In that case, Rakza 7 is perfectly fine. The only thing that I would maybe consider is a rubber that has not alot of catapult effect, but rather a moderate catapult effect (I found Rakza 7 too catapulty).
Lazer recommended Hybrid MK, thats a good one. I used Fastarc G1 and Evolution MX-S while learning BH looping, and it helped me alot.
There is not alot of reason to change rubbers though, just throwing in some spinnier alternatives that are still controllable.