Technically, all resorts are serviced every 20 minutes. That is Disney Transports line and they will stick to it.
Now, CSR actually has contracted for 15 minute service intervals. This does not always get met due to the Magic in Motion dispatch system but the dispatchers try.
CSR always came up in the dispatch rotation more frequently than other resorts during the day but at close, all bets are off.
So in reality, CSR should have a little better service but it still can be a crapshoot. POR may sometimes be a little better because there are more guests there but remember, if you are at FQ, you may miss abus or two in the morning due to full buses. This can also happen for North and East depots. Except for DTD and MK buses, all others start at the South depot and regularilly fill those buses before getting to the other stops. Even though bus floaters are staged at POR, they don't always get sent right out.