processing is more suited to making fancy visual displays
visual anything is more suited to making windows with standard user interface controls
now you could do both with either, infact its less of a pain to do graphics in VB than it is to do a standard windowed UI with buttons and menus and whatnot in processing BUT it really depends on which one you like better and suits your needs
if you need a simple application with lots of buttons and controls, visual wins, if you need a simple application that has basic controls but a really bitchin visualization of that data, processing wins.
as far as arduino, you really just need to be able to read and write data from your program to and from a serial port, both work fine