Well I don't prefer holding altcoins for long term, reason is because most of this altcoin will not do well in the future. probably you might be holding the wrong one waiting for the price to reach your target, most of them can even die in the process. I will advice if you're holding altcoin, make sure you hold the right one, so as to avoid losing money. however do you really think that altcoin will perform more better than bitcoin in time coming?
Trading altcoins is acceptable, but holding them for the long term is not really a good move, even some of the coins that at some point were part of the top 10 disappeared, and there is no reason to think a few of the coins currently there could not suffer the same fate.
So anyone investing in those coins for such a long time must have this fact always present on the back of their minds, as in this way, they will not be surprised when that happens and they can sell their coins before their losses could accumulate to dangerous levels.