recommended image upload size if going to be printing

Hi firstly thanks for an awesome product!

I want to know the best size resolution to upload bearing in mind, I want to be able to use the printing service.

My camera is 5mega-pixel and has the following size options:2560 x 1920, 2048 x 1536, 1600 x 1200, 640 x 480 and resolutiosn: fine, std, econ

my questions are twofold
1.) what size/res should I be uploading? I kindof need a min and max here as I will be uploading from south africa often where bandwidth is not great, but wherever possible i want to ensure best quality prints

2.) what size/res should i set my camera too?

thanks in advance