Depends on the Altcoin. Do they worth it? Are they going anywhere soon, what marketing they have, what APP, is it ready. How many people know about them and did they reached Hard Cap. Answer these questions and decide for yourself what you are going to do. You can sell 50% right away or wait few more months 4-5 and sell more or all of them. I think you should hold at least 10% for 2-3 years.