It's better to cover a large swathe of territory. This can hide where your general is, and every 25 turns you can collect armies from the squares. Build up that way and then you wait for someone next to you to get into a fight with someone else, or take a neutral city, and then bomb in on them in force when they can't defend, and take advantage of all of their hard work.
There's also a bit of a "dark forest" aspect to the game, where you can benefit from being hidden for a long time at the beginning of the game, but you have to trade this off with the disadvantage of not being able to build adequate forces in that time.
I'm "bubbles" in the game.
But! As both of you collect more and more area it gets really time consuming and after a point you just can't collect your army optimally. I'd argue that the biggest difference between skill levels at the highest levels is how efficient the collecting is. At that point you'll need cities. Always look for the opponent's counter to know how many cities your opponent has.
Not that it matters but I was a top 5 1v1 player quite a while ago.
The problem with attacking an enemy is that it's easy to get into a war of attrition where you both fall behind other players.
- If you begin in a corner (best) or side (ok), you can win if the side opposite to the one you are rushing towards does not rush you. If you begin in the center there is no way to win.
- To rush wait until ~17 because then you'll fill a full run before your lands get 2, enabling a second rush if the first fails.
If you win against one player before 50 seconds the chances get exponentially higher to win. Beat 2 in the first 100 seconds and you probably have 90% chance of steamrolling the entire board.
Attacking the enemy is better than taking neutral territory, n.b. you want to do this towards the end of the turn so your conquered territory will respawn.