I think mining is much more interesting for me, you can learn much knowledge about this coins, how it works and meet many friends in this community.
Yes, mining makes you more engaged into what you do than investing in altcoins. But it need certain conditions and time, right? I suppose many people have jobs and other things they have to do, so mining would be a risky idea for them. Plus, mining is also sort of an investment into altcoins, because you have to spend money of miners and electricity. To sum up, I prefer investment.