Wonder if the contractor forgot a rag or dropped something into the toilet's drain pipe while he/she was doing the work? Or he/she installed a drain that is too small or does not have correct slope. If so, the waste water would be draining too slowly causing backup and the wax ring is not sealing sufficiently. Test your toilet's drain when you remove the toilet by pouring buckets of water into it and see if it can keep up with the flow.
You could also do a quick test now by quickly pouring in a 5 gallon bucket of water into the bowl and then quickly flushing the toilet. See if the final flush drains quickly.
Assuming that the drain is clear and flows properly, I would use an extra thick wax ring with a built-in funnel to correct your leaking problem. (I think extra thick wax rings only come with a funnel.) The plastic funnel only becomes a problem if there is insufficient space between the drain flange and bottom of the toilet and the top of the funnel hits the bottom of the bowl and squishes the wax out. In your case, there is too much space between the top of your flange and the bottom of the bowl so that will not be a problem. I like the funnel since it guides the waste water down into the drain pipe.
Note that with a toilet drain that is installed to code, the water should never backup enough to even test the wax ring for leakage unless the drain is clogged or partially clogged.
HRG