There is no such thing as the best coffee roaster or best coffee supplier.
The humble Arabica coffee bean in itself has numerous nuances and notes due to its close to 1000 aromatic compounds. You just need to take note of the general ‘flavours’ that you typically enjoy or would want to explore.
Other things to note are your brew method and brew ratio. With whatever equipment you have, you need to nail the brewing process to a T. Only properly extracted coffee beans can produce a good coffee.
One of my fav coffee guys James Hoffmann who was a world championship barista with a simple, beginners’ guide to coffee tasting. He also has videos on various brewing methods to help you achieve that great cup of coffee.
I would say take note of what flavours you would prefer or is open to trying and go to a roaster and find something that suits you.