The best bang for the buck is Autel Maxisys Pro, around £1800
Snap On is a rip off for the updates, Delphi is good, but like MarkTVS said no one machine does all.
I have all 3 of those, (well actually I have the Maxisys Elite which is good for access to some hard to get on line database files but you'll not need that unless your Techie is a flasher ), they are a good arsenal for all day to day stuff.
As most of you know I also go way more in depth than just code reads and have around 12 different Dealer Level machines too, there isn't really anything I cant diagnose and fix in house, recently started EEPROMMING work too !!
Yes, for general Car Sales work the Autel will pay for itself time and again.
Beware of that Solus for that price