Gunning VS Melee

Gunning and melee have big difference:

Level-up efficiency

To eliminate an NPC fleet, Gunning normally gives you more exp than melee. To sink all enemy ships gives you more exp than just to sink the enemy admiral. But not matter how many ships you sink, the fame is not much changed.
On the other side, to capture enemy ships does not give you exp. no matter how many enemy ships you capture, you get the same exp at the end of the battle. but to capture enemy ships yields more fame than to sink them.
So if you do gunning, you get exp faster; if you do melee, you get fame faster. that's the general rule.

In term of time saving, you can take down the enemy admiral with one critical shot. or if you have a five man fleet, you can take down the enemy admiral with one combo shot. so gunning is the fastest way too. however, if you play solo, very likely it will take a while to take down the enemy admiral because their repairing is powerful. but if you assault the enemy with melee, you'll kill all his sailor on time unless it retreats succuessfuly.

PvP power in the Grand Battles

Melee is not very useful in the Grand Battles, because human players retreat from a disadvantaged melee combat quickly. plus, considering the enemy mates' powerful surgery skill. It is rare to kill a prepared human opponent by melee.

Piracy

Piracy is all about boarding and melee. If the pirate attacks a fleet and sink them, he will get nothing. The merchants do not bring arms and normally have a small crew. So rarely a pirate loses a melee combat. But with the introduction of boarding combat in the newer version of UWO, there's a further complication for the pirates. If a pirate is unfortunately looting a merchant fleet with some skilled fighters, he could be killed by the team with no mercy (trapped and then stabbed....)

Productivity

The precious items from NPC are mostly acquired by melee assaults. If you are gunning the NPC, you have must smaller possibility to get useful items. So melee is the only productive way of maritime exercises. Notably, the items are very worthy. The most valuable stuff are all from NPC plunder and Alchemy production.

Upkeep

Guns don't wear well. You may ware down tens of guns in a day which cost a fortune. Melee need armours and weapons as well, but these wear much better. With plundering skill, a melee fighter could stay in the sea forever until the food is eaten up, since he is able to get ration from the enemy ship. And after a day of melee fighting you will realize that you have accumulated a lot of money on you.
Melee consumes more food. In the early game, you may find food a tremendous expense.