I did both on the same day and while I wouldn't call it depressing, it was certainly somber.
Might be worth doing some reading (even if it's wikipedia) before the OP heads out there.

Incidentally for those who don't know. Khmer is not pronounced K-Merr as is widely prounounced, but actually K-Mai

Perhaps PNH is overshadowed by Siem Reap, where the international chains are entrenched for the Angkor Wat crowd.

Chains in REP;

CY By Marriott
Sofitel
Le Meridien
Raffles
Park Hyatt
Amansara

Chains in PNH

CY by Marriott (Jan 19)
Rosewood
Raffles
Sofitel

Hyatt Regency being built
IC deflagged

I'm probably missing a couple here and there but I don't see much discrepancy.

Some statistics, although they are totals and not exclusively higher end ones : https://asia.nikkei.com/Life-Arts/Li...-raise-the-bar

Phnom Penh, the Cambodian capital, had 317 hotels with 15,000 available rooms in late 2015, according to Bunna Realty Group, a local property company, while Siem Reap, an ever-growing tourist town developed around the Angkor Wat temple complex, had 417 hotels and 17,000 rooms. These numbers have soared in the last couple of years: A search on Booking.com -- which includes hotels, guesthouses, hostels and private accommodation for rent -- brings up a total of 514 listed properties in the capital, and a staggering 821 in Siem Reap, which has a population of just under 140,000.

CY opens in Jan, as stated, and Hyatt is being built, AS STATED. Furthermore, that wasn't directed at you but a tangential question about hotels in REP vs PNH.

Reading comprehension problems?

PNH is all about the abundant and inexpensive boutique hotels, largely located between between the Independence monument on Preah Sihanouk and Wat Phnom, running parallel to the river. There are several very charming older mansions in that area that have been converted into boutique hotels, which is also where many of the embassies are located. On my last trip, I stayed in the Pavilion hotel, which boasts two gorgeous swimming pools, as well as a few private pool suites. I ended up in a private pool suite for something like $85 a night. There is nothing like a quick dip in the private pool to cool off after a day out in the sweltering heat of PNH.

Circa 51 is another charming spot with a magnificent pool shaded by trees and very cheap rates. This is definitely the best area to stay in if you are in town on vacation. You can pretty much walk to all the main sites, which avoids the horrible traffic that has sprung up in the last 5+ years. Of course, tuk tuks and taxis are very cheap as well, but I find this to be an excellent walking city (if you can handle the heat). Definitely avoid the bigger chain hotels like IC, which are in far less ideal locations and charge absurdly higher rates. Supposedly, the airport train is now up and running (trains are definitely a work in progress here). This is definitely worth looking into, as the traffic to the airport is best avoided.

The airport train was free through earlier this year, no idea the current cost, but once at the station near the corner of Russian BLVD and Monivong you'll need to hire transportation and all the hacks and shysters hanging out there know it. Now that there's a charge for the train plus further transport necessary it doesn't appear to be an equitable travel mode. Additionally, while traffic does suck during morning and evening hours (and random hours in between), the train is not a quick mode of travel. As always, YMMV.

The two hotels are fairly close to each other, and they both have a decent variety of rooms available. Circa 51 is slightly cheaper, but you cannot go wrong with either one. Agoda usually has really good rates in SE Asia, but it is best to check the hotel website as well. It is always better to book direct if the price is the same. Enjoy your trip and be sure to check out the many markets in the area:

• Psar Thmei ('new' - art deco masterpiece w/ souvenirs and jewelry)
• Psar Chas ('old' - mostly a wet market but also a great glimpse into the community)
• Psar Orussey (mostly clothes but very large and interesting)
• Psar Toul Tom Pong (Russian market: the best place for souvenirs and gifts).

I had friends stay there a month or two ago and they liked it. Never got any specifics on the place however since we were catching up on life and drink.