I depends on the market cycle...
If a bull season will show up, i ll be selling all my alt and then get back the ones I want for long term.
However because I was a newbie at the last bull season I ended up with huge bags, I have been holding them for the last 5 months...
To give an example of holding my valuable coin is: HPB, i check the upcoming events. Depending on the event dates I plan my holding time. HPB has mainnet on 30th june and v2 launch on the 31st of december. This means I will be selling after the mainnet, wait for the price to retrace, buy back and keep until 2019