Flights are about the same price, ~$150 vs $300 on LAN.

Which would you rather fly and why?

TACA is a large international airline where as Star Peru is a small domestic one. This could help in your decision making. I get the cheap LAN local prices so have never used either one.

For the dates I was looking at it was:
Star Peru $120
Taca $323
LAN $476

Made the choice much easier

I flew TACA in Nov LIM-CUZ-LIM. My outbound flight at 5:45AM was delayed 8 hours due to mechanical problems. TACA refused to rebook economy pax onto their 10:10 AM and just made them wait in the airport for 8 hours. The only compensation was a voucher for an extremely bad breakfast at the Manos Morenos restaurant in the Lima Airport. I had a paid business class ticket and had to argue with the supervisor for about 20 minutes before I was able to be rebooked onto the 10:10AM flight (plus there was no seperate C-class check-in).

I would say fly StarPeru just because they have more flights and can more easily reaccomodate you should something go wrong, which from what I understand is pretty often due to CUZ's location and weather.

I flew Taca last year Lima- Rio. International service was fine. Don't know about domestic. Cusco is the only destination within Peru.

I always use LAN, is the best. Sometimes they cancel flights, but no often. Never took Star Peru, but though I'm peruvian, don't trust in small domestic airlines. I don't know how good is their security, mantainment, and times.