I took part in a Garden Organic seed germinating experiment a few years back.
All the seeds I tested from a variety of companies had excellent germination. However if you are looking for a 'best' brand there are other considerations.
Little seed is produced in the UK now because the climate is not sufficiently reliable and there is liable to be a lot of crop failures. So yes, seed from different companies may come from the same foreign source but the company's policies on testing and packaging are important.
Franchi packets give you a very large quantity of seeds, while T & M are decidedly mean. This may not matter for something like tomatoes where you only want a few seeds.
You may also want to consider the amount of advice available on the seed packet. Franchi gives very little, mostly in the form of diagrams, and they seem to be very optimistic about sowing and cropping dates.
Do you want a nice photo on the front of the packet, or are you happy with a purely printed envelope? Do you want the seeds packed in a foil inner packet, so that the seeds will keep well, or are you going to sow immediately and therefore do not mind? Some packets include a label. Do you want or use these?
The T & M catalogue contains hyped novelties which often do not live up to their promise. You may enjoy trying these or you may prefer a list with more familiar varieties and a calmer tone.
Personally I mistrust T & M as I am always wary of hype. I enjoy experimenting with Franchi seeds and if it goes wrong the first year I still have plenty of seed to try again. However in the main I stick to 'middle range' companies. The only company that I know sent me wrong seed is The Organic Gardening Catalogue.
Cheers,
Gillie