There are various manufacturers that make USB chipsets. VIA is one of
them, NEC is another... Various other manufacturers use these chipsets to
make the actual card that you buy. VIA also makes the chipsets
(memory/IO/bus controllers, etc) that many motherboard manufacturers use.
Note that in a lot of cases, the chipset is actually only one or two
chips.
I have used cards with a number of different brands of USB chipsets, and
have noticed no huge difference in operation from one to another.