I don't own the form two, but I own the form 6 and it's the loudest toy I own lol only because it makes such a strange noise on certain settings, like a high pitched whine or something. I definitely wouldn't call it discreet. Not sure if the form 2 would have the same problem, I guess it depends what settings it has.
The Tango is a lot quieter than my form 6 and is the most powerful toy I've used (other than a mains powered wand, but that wouldn't suit your need for discretion). Because it is so deep and rumbly yet still has the buzzy feel a lot of people crave, even on the lowest setting it is powerful and it is quiet for how strong it is. There are quieter toys, but you might find them lacking.
I'd reccomend the Tango as both the more discreet and more powerful option. It's very popular here, and with good reason :)
Plus if you bought one and found it didn't suit you, there is the years free returns policy!