I am currently using Transparent Ultra XL bi-cables and can highly recommend them. They are not cheap, but are very very good.
The new MM range is better, however they are more $'s. I always think you should aim as high as possible in terms what you can afford - but that does not necessarily mean you wont upgrade in the future
I actually use Transparent throughout my system, from power to interconnects. As you go up the range there are large improvements, but the cost increases substantially. I have settled for a combination of mostly Ultra cables (I have a couple of plus and a digital reference cable).
Best advice as always though, is simplyto try them in your system.
Rgds
Marc