Bad threading behaviour in perl isn't much of a problem these days. Listening to my managers/salespersons/cleaning staff, these days you do most stuff "in the cloud" (e.g. as webservice) anyway. And on webservers you don't thread, you fork 8-)

More seriously: I my opinion, the best way to choose is to learn the *basics* of both and try to code small routines you would need in your project. The language that causes the least hairloss (or grey strains, whatever rocks your genes) will be the language of choice.