External devices are NOT better than PCI devices. They are more convienent, and the life expectency of the PCI bus is limited as PCIe comes of age.
Given your mixer (and from that choice, I expect that the rest of the system/mics/monitors/room are of similar quality) you will be well served by any of the obvious choices out there. If you are seriously interested in high quality, a much higher dollar investment is required. My own favorites for low-mid budget work are RME and Lynx, but these are a few dollars more than your limit. M-Audio, Presonus, Tascam, Terratec and others all have workable options that will not shame you in terms of sound quality. Most of the major players are so because their gear works, and sounds decent. Additional costs buy better service and support, fewer compatability problems, and often more ease of setup and use, allowing you to be more of a musician and less of a computer geek.