I think altcoin mining is more profitable than mining bitcoin because the difficulty level of bitcoin is so high so you need more powerful miner to get the enough rewards.ASIC miners is the only option to mine bitcoins and it needs big investment also.So you can do altcoin mining for example Monero is one of the best altcoin to mine because their mining difficulty is low so you can install GPU miners to mine monero and then you can trade your monero for bitcoins.