Autosmart tardis every time!
But be aware this should be done as part of a process. It will remove any polish / protection you have on the car.
You will at least need to wash the car afterwards to remove the excess tardis and then dry and polish the car.
Ideally and for best results you would follow the complete process:-
1) Clean car as usual (prefferably 2 buckets etc)
2) rinse
3) Autosmart Tardis
4) rinse
5) Iron cut type product (this will remove any metal contamination)
6) Clay bar - If you want to save time then you can combine 5 and 6 by using Gyeon products.
Most clay bar will fall apart as its not compatible with the iron X but Gyeon have an Iron and clay that work well together. Thats what I use and its great!!
7) Rinse
8) Paint correction if required.
9) polish and protect with chosen products