In all the years I have been a car owner ( wow that makes me feel old) there is no substitute for a proper hard wax polish and some elbow grease.
My garage is full of all sorts of types of polish and wash waxes that I have bought over the years.
I have although found that Maguires clay bar system is good but I now use Autoglym high definition wax.
Like everything you only get out what you put in and solid wax is not as quick as some polish products to deal with but the results I get are superior to anything else I have tried.
I use Maguires gold shampoo, not cheap but worth it.
I also have found that there is no substitute for hand washing with a mitt and using 2 buckets, one for shampoo the other to rinse the mitt.
And yes I have a nearly new power washer with brush attachments that would only scratch the paint so its used for removing the heavy grime and rinsing off after washing ( no brush)
Hope my Mrs don't read this or else she will look in to my garage cupboards and no doubt complain at the money I have spent.