If you search the site for threads on fast tans you will find lots of info.
There will be threads explaining that fast tans are not fast because they give you colour fast, they are fast because you wash it off fast.
You will find lots of oppinions of Sienna X tonight's the night & many other brands fast tans and that they tend to not last as long as a 'normal' solution - there are exceptions to the rule but they are only a few (veloci-t I believe is one of these although I've not tried it personally).
You will find threads where people have thought the solution didn't work then 24 hours later they announce they do have some colour, there are threads upon threads of info all waiting for you to find them and read.
As for asking which one is best - that is a minefield as each therapist will like different things and therfore you will NEVER get one answer from all, you will get loads of recomendations but in the end you need to trial them for yourself to see what you like and what you don't and then go from there.