We just had this issue in the 310 - the Collins transponder was acting up. After some 35-40 years, I suppose it had a right to. Rather than messing around with it (which is typically a money-losing proposition), we chose to have it replaced with the GTX327. It was about $2,200 installed. I would highly recommend the shop we used.
I've used them in a number of aircraft over the years, and never had a problem. the Aztec has one, also. It is a great unit.
We chose not to spend the extra cash on the 330. The TIS doesn't help us where we spend most of our time flying, and it would have represented a significant increase in costs. Since it still needs an upgrade in order to support ADS-B and who knows where things will be 8 years from now (I am figuring it will probably be time for another upgrade anyway), we'd wait and deal with it later. We'd like to have traffic, but TIS only works in certain areas - mostly where we don't fly - so if we get some traffic, it'd need to be TCAS.
I'd go with the 327.
