Gunboat is the tactical aspect of the game without the influence of lies. It's sitting there, looking at the board,trying to guess what your opponents are going to do with no information to go on and knowing they're doing the same. A lot of a normal game of diplomacy is about playing the player behind the country and in gunboat, you don't get that. It's purely a chess game.
Public Press is what I consider the ultimate form of Diplomacy. It is by far my favourite variant because it represents how diplomacy works in the real world. There are no secrets, its your ability to convince someone against another's, all the cards on the table. You get in a game with six people that know how to talk, and it will easily become the most difficult and most rewarding game you've ever played. Too many normal games are reduced to abbreviations and minimal caveman speak, public press REQUIRES that you know how to write with poise and power.
The variants aren't for everyone, and for the purists out there, no Diplomacy exists but regular. Give them a shot, you might find out you like them, you might even learn something. My plethora of gunboat games helps me recognise the best moves to make regardless of the press involved, so instead of the press dictating my moves, my desired moves dictate the press. And public press makes you measure lying much heavier.