Hi,
In a nutshell:
As far as I remember, TestComplete supports more native Windows technologies than TestLeft. TestLeft does not support Mobile testing. Also TestLeft is licensed on the per-year basis while TestComplete license is perpetual. There is no NameMapping/Aliasing in TestLeft which uses Models instead (the same conceptually but less handy/visually clear/manageable as for me). Test assembly created with TestLeft contains assemblies from TestExecute core that are not allowed to be distributed to the third-party customer - i.e. you are not allowed to provide your test assemblies to those who does not have TestExecute license.
