I disagree. Yarmolenko is higher reward (higher risk too) signing. He's younger than NOlito and has higher ceiling. We need to act more like Madrid and start buying younger players, not forwards like Nolito who might have just 2 years in them on top level. And Yarmolenko shouldn't cost more than Nolito in winter, he'll have just 6 months until the end of his contract so he will be cheap.
More interesting is how will we play him if he comes. If he will be super backup for all 3 positions or will the tactics change to acomodate him (like when he replaces Suarez will he move to center or RW and Messi will go to his old False 9 position)?
We also have to consider the fact that he'd be joining in January, the beginning of the most crucial part of the season.
I get that he has higher ceiling, and agree with it whole-heartedly. But, if we consider when he'll be coming in, we can't let him have a period to start finding his feet, as each passing match gains more importance. That's why Nolito would be a better signing. Lucho knows the player inside out, and knows what he's getting. Nolito will integrate into the squad WAY more quickly, and won't have to adjust to a new league. There's no language barrier, adapting to a new country, etc.
And anyway, from Yarmolenko's POV, this move doesn't make sense. He's a RW, and isn't that effective in the other positions (from what I've seen). Messi will always play as much as possible, so he'll get even less minutes. Nolito will be a like for like replacement for Pedro on the LW, which is what we need.