In my opinion, i would put 20% on eth, 30% on xmr, 20% on siacoin, and 30% in waves. that is a profitable porfolio with good and solid coins, guaranteed profit in a few months.
I wouldn't necessarily put my money into those coins or in those ratios but you are right that generally diversification gives you a more stable return.
The only problem with diversification though is that it's hard to hit it big since your profits will be much less than if you had gone all in.