VAC has a wide variety of songs ranging from harsh electronica to mellow, trance-like riffs. So, no, not all VAC songs sounds similar to me.
As to which album you might want to buy, it mostly depends on your taste in electronic music: harsh or mellow? If you prefer harsh electronica, I would suggest a lot of the old albums such as Between the Eyes volumes 1 and 4, and Hex Angel (Utopia-Dystopia). Or, if you prefer the more mellow stuff, check out VAC's newest album: Lust for Blood. Regardless, Fun with Knives is a great album that blends both of these styles together, so you really can't go wrong with that album.
Good luck in your search for all the great VAC songs (there are a lot of them) !