Joining a guild is one of the most important decissions you can make on Seafight. Once you reach a certain level, you will need the help of others in order to complete your pirate tests within the given timeframe. If you are new to the game, some guilds will also help you by sending you gold, so you can buy the elite design (Terror of the Seven Seas) from the market cove.
There are many advantages of joining a guild and many disadvantages of not doing so. Which guild to join is entirely up to you, but once you have recieved help from a guild, keep in mind that they have spent their own time on it and you should help them as well whenever you can.