It's difficult to compare a host-based system like PTLE with a native system like SONAR.
Your friend can't give away or sell his/her copy of SONAR, according to its licence agreement. It's up to you whether you want to continue using this in violation of the licence, but remember, there is no free lunch.
SONAR is only available for PC.
There are many great interfaces. The RME Fireface is one of the best, and MOTU and M-Audio are among many companies that make competitive units. With proper computer setup and usage, any of these can sound great and have rock-solid performance.
SONAR is a great tool. Objectively, it has more features, especially with MIDI, than PTLE. IMO (even if you pay for SONAR, SONAR with an appropriate interface will be a better value than PTLE, but you can make great recordings with either.