BB FANS

I've recently stored a few processed pictures as uncompressed TIF files but the print size drops so I guess the DPI is lowered.

So what is the best recognised Loss-less format to use ?

I normally take the pictures in Raw (.NEF) format which is basically a Digital Negative and store processed images as Paintshop Pro (.pspimage) but if I want to submit them for say a competition this format won't be recognised.

For example the full 6.2MP 300dpi image is just short of A3 but the same image stored as .tif is around A4 and that's on two printers (HP & Epson) with settings set for high grade Photo Paper and Highest print settings so something is lost in the file conversion.
I think the .tif is retaining the 16bit data and not converting it to 8bit like lossy .jpg does. And I can't see a DPI setting for the .tif format.

Any ideas what the best option is ? I know when it comes to competitions it's ultimately down to the format they accept.