Both are good planes but Tejas has been in development for 30 years and we still do not have one operational squadron. Tejas initially was supposed to replace the aging Migs of the Indian air force but repeated delays has ensured that plan will not transpire and the Indians are still flying the MIGs and probably will be for the foreseeable future. The Tejas once again is a good plane but it might be too little too late as other the IAF is busy looking at other air crafts.
JF-17 has the similar objective its suppose to replace the F-7s and the mirages but the difference is that the JF-17 program is progressing smoothly. 3 squadrons are already operational and now a squadron of Block II aircrafts is introduced. The JF program has matured alot since its introduction and will continue that trend until block III is introduced.
So to sum it all up I think the Thunder currently is a superior air craft. It was built with direct involvement with PAF which means all they would have done whatever they could to make the aircraft better. JF-17 It has been in service for years, is built in numbers, has a substantial weapons package, and its operationally being used for COIN operations. So keeping everything in mind I will give the nod to JF-17.