Regular exhaust tips will have no effect on the sound... Those would be strictly for looks and definitely a must because these cars look good with a nice set of tips.
Resonated tips are more expensive and don't do too much to tone the sound down. I would say buy a set of them if you find some that you like more than a set of regular tips.
I would make sure the shop that does your work removes the stock resonator neatly in case you don't like the sound of it... This way it can be put back on with little effort.
Here is a shot of my tips on a stock exhaust...