Pre-mades would be the most competitive, but only if you have a pre-made team. For the rest of us that just want to be able to log in and play a close match without one side dominating the other the ladder is our only hope.
Currently neither of these options are really avialable. The Clan Wars content will give us pre-made vs pre-made, Custom currently leans towards "me and my friends" vs some random people.
And Pantheon and Skirmish have to few people waiting to play to have some real matchmaking going on. Let alone the messed up stats. I mean they added the feature to see how many others are waiting for a game and when there is only 3 other people and it throws me in a 2 vs 2 how much match making was really going on there???