What is best omega seamaster or rolex submariner?

It depends what you mean by 'best'. Rolex make their own movements whereas Omega use ETA and add their expertise. I have had 3 Rolexes, 1 Breitling and I currently wear a Seamaster Professional Chronometer (James Bond watch) daily plus it's waterproof to 1000 feet, which is handy in the shower! With Rolex you're paying for the brand name and the kudos, so my answer is they're both absolutely great watches, it depends how deep your pockets are. I wouldn't buy an Omega, Rolex or any other 'high end' watch from any auction site and be wary of any watch that doesn't have paperwork, boxes etc, as no-one ever throws them away. If there's no paperwork and box then it's extremely likely to be counterfeit or stolen. If stolen, then when the watch is serviced (they have to be every 3 or 4 years) it will be checked against the stolen register and you won't see it again. Rolexes and Omegas are always expensive, so be wary of any ridiculously cheap watches as well. Rolexes and Omegas simply don't cost £100.