Source: Lexxaa
Also, picking a race faction you may not be exalted with yet makes grinding that rep a LOT easier, since you get rep for turning in the dailies, and opens up that race's vendor sooner so you can hand in those scroll things. i've decided to do the last 2 race's im not exalted with first, so that completes the grind across all 5 faster. |
Also, if you move on to a new faction that you are exalted with you will gain rep with other city factions that aren't maxed quite yet. The only problems are that you don't have a choice about which it is and it's at a much lower gain.
Once I had opened up the Valiant dailies for Org I started gaining rep with Darkspear because I was already exalted with Org, TB and UC. I hit exalted with Darkspear before getting 25 badges and moving on to SMC.
To answer the OP though, once you've done the quest to become a Champion of your city you get to pick your next city since all the other factions open up to you. If you really wanted to, you could just continue to collect the badges with the one faction you're working on and not move on until you're exalted. Just be sure not to turn in the quest for 25 badges as that finishes the chain for that faction.
Once you're a Champion with all the factions you are no longer able to pick up those dailies and have to rely on the actual Argent Tourney dailies that reward the scripts/coin purse to bump up your rep through that turn in.