I wouldn't really worry about the brand of the card or the software they
come with. It all comes down to the tuner and the chipset. For years the
bt848/878 chipset has been pretty much the standard, (Prolink Pixelview,
Leadtek 2000XP, STB etc). Conexant has recently released a new chip the
CX23880 chip (MSI TV@nywhere, ASUS TV tuner) that looks like an improvement.
Pretty much all the programs that come with the cards are downright
pathetic. My Pixelview card, I wouldn't even put the CD in my drive the
contents are so bad. Many far better 3rd party programs exist with much
better capture capabilities. The ones i've had most luck with are
VirtualVCR, VirutalDub(Mod), PowerVCR, but analog capturing is really a bit
of an artform, and you've gotta get a handle on drivers, compression codecs,
audio sync etc.

My advice to you would be keep the STB card (for now), get the btwdmdrv
drivers http://btwincap.sourceforge.net/, you've already got DScaler for
watching TV, get VirtualDubMod for capturing. Seemed I had the best capture
results with VDubMod (least sync problems), using either the PicVideo MJPEG
codec or the hufyuv codec.