Trading on bitcoin is slow and requires a bigger fund because bitcoin is costly so I prefer trading on altcoins. There's so many altcoins so there's fun in choosing the ones you like.
Both Bitcoin and Altcoin have great potential and both are profitable in trading. This only depends on your planning. Are you a long term trader or a short term? For long term trading, you can choose Bitcoin which has been very profitable since long. For short term, Altcoin is the best option and gives good returns. Besides, you can do the math yourself as well. Try checking out the market graphs and figures and keep moving.
Yeah they are both profitable in trading but it has different characters altcoins is good option for short term investment while bitcoin is good for long term investment, while you earn in your short term investment you should set aside and turn some of it to bitcoin for long term investment while the BTC price is low.
If you are really looking for a good way to earn like double your investment in short amount of time? then there are a lot of alt coins out there that can give you that opportunity, you just need to analyse the coins and get lucky to get in when it is still cheap and sold them on the right time.
As for bitcoin, much better to hold long term, at least 6 months to a year will be good, so if you have that mental toughness not to be tempted and just totally forgot about it and just go back after a year and revisited your investment, then Bitcoin will be a good coin to hold and invest for a long time.