Essentially what you need is a crystal ball/seer/soothsayer.
In a bull run it's easy to predict "coins" that will rise in value, because one way or the other, all altcoins are linked to the value of Bitcoin. When Bitcoin rises, so will the altcoins, or the majority of them at least.
The same holds true for a bear run (which we are in right now) only in reverse. It's easy for me, or anyone else, to predict that the value of most coins will fall in value, which they are currently in the process of doing.
That being said, if someone did suggest a coin to you and you went off blindly mining it, even at the expense of earning less than you would mining ETH. Would you begrudge them if you mined it for a week/month/year and then it ended up being worth nothing? Would it be their fault for suggesting it to you? Or, would it be your own fault, for not doing your own research in the first place and seeing what options are open to you, rather than taking someone else's advice.
If mining ETH is the only profitable coin for you to mine at the moment, why would you mine something else at your own expense when you can just buy those other coins with your profits from mining ETH?
For example: In one day I can mine with thirty 470's and get €18.83 in profit from mining ETH in one day according to this
https://crypt0.zone/calculator/s/s01wqjhgBut if I want to mine Dinastycoin (DCY) I would only earn € 6.20 in profits per day. So wouldn't it make more sense to mine ETH and buy over three times more DCY with my profits from ETH, rather than mining DCY for the day?
I guess it comes down to this, do you want to speculate with your own money, and are not interested in mining for a profit, then just buy the coins and forget about mining, or do you want to speculate with your profits from mining at no extra expense to yourself.
If I suggested to you to mine DCY (which I wouldn't) and you went and mined it, every day you'd lose over €12 in profit compared to mining ETH. Do you think that by mining DCY everyday for a month is the right choice? €12 x 30 days = €360< that would be your loss per month compared to mining ETH. If you believed that it was still worth it mining DCY even at that loss, because you believed it would surpass ETH in value. You could have bought an extra €360 worth of DCY in that month if you continued mining ETH or the most profitable coin and used your profits for speculating.