I would recomend you to evaluate the main softwares available, looking for the main issues you want on each of them. Most of the piping stress software are very easy to use, depending on the way you work or prefer to organize the job run. If you usually run big and complex systems some extra edition features like copy, mirror or rotate block operations would be very useful.
Several years ago we have performed this kind of evaluation ranking the main features we want on a piping software: nozzle loads check modules, flange check module, structure modeling, substructuring, CAD interface facilities, WRC-107/297 calculation and others, dynamic analysis features, capacity to run complex jobs with several non-linear restraints, technical support, input facilities and several others. You have to judge what things are more important considering the cost benefit (do not forget the annual update).
Nowadays we have been using CAESAR II and TRIFLEX.