It all depends upon your desired outcome.

Buying BTC would be the most profitable if you're looking for the greatest opportunity for ROI. If you're feeling a little altruistic, believe in supporting the BTC network, enjoy tinkering with hardware as a hobby, but would be ok if you potentially got out a little less than you put in, then give mining a shot. Maybe it's a combination of both mining and buying to diversify? However, if you have free electricity and you can run your miner indefinitely, you shouldn't have to worry about taking a loss by mining - but it likely won't end up as profitable as buying BTC outright either.