If you are primarily doing at-home / studio recording, buy an 8-channel interface. I have a Focusrite interface and recommend them highly.
If you are primarily doing remote / on-location recording, buy an 8+ channel standalone recorder like those others here have recommended. These devices will be much more stable in the field and less error-prone than a computer-based system. Yes, some of these function as a computer interface as well, but I woudn't even bother with that during recording. Just record to the dedicated device and dump it to your computer for editing later.