It always depends on what your job is. Don't let the other comments fool you. There's a time and a place for RGB. It's usually used for visual, non-printed media (like the web or video) but under the right circumstances, RGB will give you more color... but only under the correct conditions.
First, your question about setting your best quality for images. AlphaGraphics has a small tools section for free profiles. As a printer (they print both digitally and off-set, which is dissimilar to the competition -- Kinko's for example), they have created presets which work as a great starting point: http://us000.alphagraphics.com/tools
is the URL for downloading Application Color Setup files for Bridge (which the rest of the Creative Suite uses), and PDF Creation Settings Files for Distiller and InDesign.)
I don't consider these anything more than baseline templates. They are good for everyday work when prepping your files for color output as well as for outputting for PDF, but they are by no means perfect for everyone. They're just a jumping off point for you to edit and configure for your own needs (and the needs of your printer.)
When it comes to RGB and CMYK, here's my response to nearly every designer (take them as you will)
• If you are printing as a proof on a digital machine and are expecting your FINAL work to be offset (meaning a printing process in which an inked impression from a plate is first made on a rubber-blanketed cylinder and then transferred to the paper being printed -- from a printing press), I would output for CMYK so you can proof your colors as close to your intended final output. This doesn't mean that if a job is 4 color that you can't output in RGB while proofing, but if you're going to design your work for off-set printing, it's probably best for you to set all your images and your document profiles as CMYK from the start. That way you have no surprises like a single image that's still RGB which will cause you problems for later. If you have a job with photos (like a catalog) that is 4 color + spot colors, you would be better off looking at it as you intend it: CMYK.
• If you are expecting to anything that will only go to a digital printer, like, for example photos or a student portfolio, then I would suggest RGB because of its wider gammut of colors for digital printers (like a Xerox, Canon, and maybe even an HP -- but Xerox and Canon are the big 2.) So if you're looking for BRIGHTER, more vivid color, gear your designs and output for RGB.
I should point out that these are not rules -- there are almost never any rules (unless you're working off-set.) Then even at the last moment, the printsmith has the option to change them. Most designers who would see your question would say CMYK always, because they're expecting your job to go to an offset press, because that's what they're used to designing for professionally. They're used to putting together a four color job plus 1 or more spot colors along with a varnish and maybe even an embossing plate. It can be very detailed. But if you're working on a job that will only be printed digitally, I would suggest test-driving your job as RGB -- you'll find your images don't look quite so smoky and will achieve more vibrancy.