With World of Tanks I did mostly the former, running up the German tank destroyer and heavy tank lines exclusively at first, and then when I reached a plateau I started up the light and medium tank lines, etc.
In World of Warships, because I got in on the Humble Bundle Bungle and have so many port slots open, I decided to cast my fleet net wide and have lots of ships from both tech trees. While it means I level up my main ship lines (the IJN battleships and carriers) more slowly I still get experienced with what the other lines and nations are capable of and I tend to make a lot more credits as the big money makers tend to be lower-mid tier ships and not the higher tier ones.
With the Russian destroyer line and German cruiser line coming, I plan to add them to the rotation... sigh, and I might as well get the American destroyer line going.
As the grind goes, having lots of ships with different play styles to choose from has kept the game fresh for me. Taking the Nagato in a battle with experience players is very different "clubbing seals" in a battle with newbies with my Kuma (an amazing little ship BTW). Still, I'm getting closer with the main two, both the Nagato and Hiryu are around 100K experience racked up and the tier VIII ships are ~132K required. I estimate getting to them in another 15-20 games each which should take a couple weeks. The good news is that I have all the credits required for one of them straight up without selling anything.
I had the tier VIII Amagi in closed beta and remember enjoying it, and I feel I'm a better battleship captain now than I was then, so all indications point to that being the ship I purchase, and I'll probably use free experience to get out of the stock hull. In World of Tanks, the gun was often the delimiting factor to success, but in Warships I find the hull is.
Whether I get the IJN Shokaku is up in the air and depends on how the ranked battles continue to play out. You see, you can only use tier VI or VII ships in the ranked battles and to get both the Amagi and Shokaku would require my selling of the Nagato and Hiryu, my main ships for ranked battles. I'm hesitant to do that because I've been enjoying the ranked battles and the Shokaku doesn't have any major selling points over the Hiryu; sure, better planes but also in higher tier battles.
Speaking of ranked battles, I've been having lots of fun in them. Since the teams are smaller (seven per side instead of 12) and the composition more tightly defined (only tiers VI and VII, max one carrier per side) AND the battles are domination mode with a cap of 800 instead of 1000, I find the battles tighter and bloodier since you pretty much have to take a cap or find yourself outscored too fast. In regular random battles, you have time and lots of dumb targets to keep the score close without jumping on the caps.
I've done 32 ranked battles and have a 62.5% win rate, helping me up to a modest rank 18 (lowest starting rank is 25, highest possible rank is 1) . I'm far more dangerous in my Hiryu (11 battles and 9 wins) compared to the Nagato (19 battles, 9 wins) and I think that is due to the far fewer number of cruisers (typically 1 or 2, rarely 3) so less AA and only one opposing carrier so unless its a Air Superiority Ranger or Hiyru I know I have fighter parity or superiority, and even when I don't I find the holes in the air defense to drop some torpedoes and bombs.
The only downside to ranked battles is that the wait in line can be longer due to a smaller pool of players to select from with more strict team composition rules. When I run into a wait longer than a couple minutes, I just jump into a random battle instead and run with the plebes :)
Next week I'm going to take a review of all the current maps and thoughts on them.