Power Generator - Cheaper, more range but bigger negative impact circle.
Wind - purchase expensive, less effective range, less yearly power costs and smaller negative impact circle
Solar - purchase expensive, less effective range, less yearly power costs and no negative impact circle
Personally I think one of the first mechanic researches to complete in challenge/franchise.
Usage really depends preference.
If you have big enclosures in 1 spot, a generator could be more effective - you can easily place it out of the range of visitors - you don't have to place solar panels all over the place to get the same range. Placing more, ofc. requires a bit more maintentance efforts from your mechanics.
In the long run, solar panels are cheaper in operation costs. And you can easily place them in your zoo, without much hassle.
Not bothered by its appearance/look in my zoo, but some people don't want that many facilities in their zoo.