depends what you want from the motor
if you want to produce GOBS of boost and plan on extracting huge amounts of power, than running low compression pistons will allow you to run A LOT of boost with a larger region for error, however super low compression motors are basically all or nothing- if you're not into the thick part of boost, you're motor is going to feel completely bottom less- this setup will be best if you just like to go fast in straight lines and don't care about sacrificing around town power for maximum power on boost
medium compression pistons will result in decent driveability at low RPM's when you're out of boost and still give you a decent amount of safety when it comes to tuning at higher boost levels- using stock pistons from the ls would give you decent power off boost and still leave you plenty of room for error- this is probably the best combination for street/track driving
bumping up your compression significantly and running a lot of boost can be tough, and means you'll have to have a DAMN good tune on the motor- but this will allow you to run less boost to reach the same power levels and will provide nice reliability off boost- this combination will be hardest to tune
of course everything i've written depends A LOT on what turbo you plan on using and at what boost levels, etc- it really all comes down to what you're looking to get out of the motor and what type of use the car sees
