Use a PDF workflow, Onyx supports it pretty well. All other options have downsides. PDF/X-4 is recommended usually though I think the SWOP color space is a bit small (I calibrate my own color spaces and created my own workflow). Illustrator->PDF, InDesign->PDF, Photoshop->.tif (with embedded profile, again I use a custom color space). You could go Photoshop->PDF too but that gets a bit silly as all you're doing is encapsulating raster data in a PDF.
Downsides to an all EPS or TIFF system:
EPS - No color management, large file sizes
TIFF - Rasterizing before it hits the RIP (not ideal), large file sizes, and unless you're rasterizing at full dpi won't be as crisp as it would be maintaining vector to the RIP. Also creates production files that are hard to modify in the future, causing you extra steps for minor changes
Of course you'll need to learn PDF preflighting but that's another thread. Now if art comes to you already as an EPS, go with it, same with an image (jpg, tif, etc.). No need to convert into a PDF then unless you want to fit it into a specific preflight workflow (say if you like doing color management conversion pre-RIP).