You don't get a "chance" at exotic at level 25, what you should get is a new quest line, upon the completion of this quest you will receive an exotic class item for your character with the relevant faction. It will be light level 290. Each faction has 3 ships, 4 shaders and around 8-10 emblems. These are only obtainable from faction packages. So when you should change factions really depends upon what you want? Are you interested in getting all three exotic class items? Or do you want to collect all shaders, ships and emblems from one faction? If you just want the three exotics then I recommend changing factions the moment you hit level 25, you can complete quest line whilst representing another faction, weird right? Just know you can't put your new exotic on unless you represent the corresponding faction. Also you need a legendary class item from your faction to complete the quest so make sure you have one before you change factions. If however you want all faction items shaders, emblems etc and you haven't got them all by level 25 than you should put your exotic class item on to give you more faction rep and keep chasing them items. If you are early on in the game it might be worth your time getting each faction to level three so that you can purchase their wares, some of the better rolled vendor weapons have only been available at faction vendors in the past. If however you are loyal to your faction than you should never change, you should never even contemplate looking at another faction vendor.

Never... [spoiler]NEW MONARCHY FTW!!! [/spoiler]

Im sticking with fwc because looks and well... Me. But I swapped to new monarchy to hit rank 3. Got it almost leveled to the next. Then swapped back to fwc and did the same. So when the update drops. I donate to NM for the faction package. Swap to fwc. Donate again. Go on my warlock and donate to DO. Faction package again. Complete a strike on my hunter or warlock(can't remember which) package there. Hunter has a crucible package waiting. Titan a vanguard package waiting. Got lots of shit to pick up. Yayyy

Well, now with the update, you will be getting higher light gear with the factions. This is why I stayed with DO, so I can get my gear ranked up.

Rank 90 with New Monarchy with my hunter

Whenever you want, you can revert after a week. But there's no point unless you really want gear from both and don't want to have three characters (one per faction).

After you get everything you want from the faction. Get all the shaders, ships or exotic class item you wanted? Go ahead and swap

I just switch as soon as I hit 25 and complete the quest for the exotic, no reason to stay unless your collecting the ships or shaders.

FWC FOR LIFE! [spoiler]...that is all guardian lol[/spoiler]

Tomorrow

After you've gotten every thing from that respective faction. I have every thing for every faction and I'm about to get my last exotic cloak c: After that I'll just stick to one faction

Aim for rank25 to the exotic! Get all the ships and shaders then move on!

Switch when you are complete the quest you get from rank 25