the simple difference is that if you buy you will not have more bitcoin, but only more fiat in the case bitcoin go big
if you mine you will have more bitcoin, if you sell your equipments back at certain point
i would buy if the roi is very very long, otherwise it's better to mine, both have their risk
I think it will vary on the situation if the value of bitcoin are going low it is good to buy then wait for it to go sky rocket high so you can exchange it to fiat to claim bigger amount, but you can profit in mining if The biggest factors determining profitability are equipment costs, the price paid for electricity and the value of the bitcoin you mine. it is certain that it is good to mine because the price is high but it electric and equipment cost will still vary depending if you would ROI from it!