I'm surprised I've never come across this on the forum.
I am currently in the midst of my second trip to the Philippines. The first time was six months ago and was solely in AC.
Exchange rates are competitive. I usually use Norma's Exchange, but most other places are equivalent to Norma's and I found one place on Walking Street, close to Club Asia, that's even a little higher.
All the places in AC have the rate clearly posted prominently as well.
When I got to Subic Bay, none of the places had the rates posted and in most places you have to do a song and dance to try to negotiate a better rate. For example, in AC, rates were betwee 43.70 and 43.75, but places in Subic were offiering 43.30-43.35. If you searched around, you could get 43.50-43.55
I just arrived in Manila today. On, and around P. Bugos Street, none of the places have the rates on display. I inquired at two places. One stated "43". I responded, "Forty-three point what?". He said, "It's a flat forty-three". I only checked one other place and they quoted me 42.5.
I was advised by the car service at my AC hotel to exchange in AC as rates are better there and we stopped at Norma's. I think I have enough on hand to get me through three days here, but if I run short, I'm going to have to either go to an ATM or deal with the ~43 rate or whatever I can negotiate.
To put this in real cost, 43 vs. 43.75 is 75 pesos per $100-bill, or about $1.75 USD more for each $100-bill exchanged.
When I checked into my hotel at the Antel Best Western, even though it was pre-paid through expedia, a 3,500p deposit was required for consumables. Given that I assumed the rate was lower here, I asked the receptionist if I could leave a $100-bill (valued at over 4,300p) as my deposit instead, and of course, the $100-bill will be returned to me upon checkout, unless of course I trash the place 
TL;DR
AC seems to be the best place in the Philippines to exchange currency, so overload there.