Just to nit pick, they are not carousels as carouses only have horses, but yes, these kids round-a-bouts are everywhere. They're expensive and last only a very brief time, after which the kid wants another go, and another, and when you have to say no, because you can't afford to put another £2 in, you are faced with a screaming fit. For that reason, I have to say there are no 'best', and they are all as bad as each other.
I hate these things; so often I see children sitting n the at the shops, their parents unwilling or unable to put in the coins. Sometimes the little mights jump on them of jiggle in them hoping they will do something and all the children get is disappointment.
My grand-daughter was happy just to sit in them & ‘play’ She never asked for money to be put into the slot. Once a women was putting her son on 1 & putting in the money, & she asked if my granddaughter who was sitting on a nearby seat with me, if she would also like a ride at the same time. ‘Yes please” was the answer to that one.