"farming" refers to playing or simming the same battle over and over to collect shards. if i'm farming the slave i, i'll run that battle over and over until that ship reaches 7 stars. the "best ship" is not objective. you can decide what would be best for you based on what would work with your existing ships' synergies (like if you have a couple other good galactic republic ships, another galactic republic ship would be a good addition to your fleet), ships that seem powerful/useful to you (look at their abilities, what other players are using, google if you're between a few), you can make posts with your specific ships/toons and what's available to you on the swgoh subreddit or forums and ask other players what would be best for you, you can also farm the ship for whatever your most powerful character who can fly a ship. what counts as the "best ship" is very subjective and dependent on you as a player.