First of all, not all ethernet chips are created equal. There are simple ones with the bare minimum of buffers, and more sophisticated ones that have large buffers and pull a handful of tricks to make better use of the PCI bus.
If you're not piling up LAN channels to build a server, that hardly matters. With at most two 10/100 channels in a typical computer, you won't notice the difference.
Building a "generic" 10/100TX card isn't hard anymore. Buy the chip from one of the usual suspects (Realtek, SiS, whoever), take their reference design schematics, make a PCI card, and you're set. Chip maker's reference drivers will apply, and from said two companies, they're OK.
Now what does the more expensive 10/100TX card give you? Maybe more feature packed software, remote management stuff, longer warranties. Nothing of those matters for the normal user.
regards, Peter