From 1 to 10 Rate the Customer Service of these Companies

GoDaddy - 3 (only phone and live chat left after the removed the critical email support)
Sedo - 4 (not that much experience with them. But not satisfactory. I think their website is a mess)
Moniker - 0 (what support?)
Flippa - 5 (again some but not a lot of experience)
NameSilo -8 (I personally don't use NS, but have always found their support to be speedy and excellent)
NameCheap -7 (no complaints here)
Pheenix - 7 (replies usually within 12hrs, but always had relevant replies)
Name.com - 8 (I have only a few domains here. But support is always speedy and excellent)
Afternic - 7 (domain conflicts are resolved extremely quickly. Less than 24hrs)
Dynadot - 9+ (but then I do have an account manager here)
NetSol - <1 (awful. absolutely awful)
Above 6-7 (satisfactory. only open in Aussie timezone, M-F)
eNom 6 (satisfactory. not great but satisfactory)

These rating are basically based on email support, and if that not available then their support structure on their website (ticketing system, not live chat).

GoDaddy.com - 8
Sedo.com - 8
Moniker.com - 1
Flippa.com - 8
NameSilo.com - 7
NameCheap.com - 7
Pheenix.com - 5

One last comment I should have made. I'm geographically half a world away from the US. I'm usually sleeping when the US is awake, and vice versa. So if some of the times I quoted above, seem long to you (to be acceptable) it's because of the geographically distance between us. It's not because they seem slow in their replies. You learn to have a little more patience - else you'd go nuts

GoDaddy - 3
SEDO - 2
Namesilo - 8
Flippa - 6
Namecheap - 9
Pheenix - 8

My ratings are based solely on email support and/or chat

GoDaddy.com - 4
Sedo.com - 5
Moniker.com - 3
Flippa.com - 2
NameSilo.com - 6
NameCheap.com - 8
Pheenix.com - 2

These are the ones I have dealt with most often. I didn't rate any from your list I haven't had any experience with. I added a couple not on your list. These are from my personal experiences and not based on what I have heard or seen from others. These ratings would be different if I took into account what has happened to other users here that has been reported.

GoDaddy.com - 7 (Domain related Services Rating, Hosting would get a different score)
Register.com - 2
Maddogdomains.com - 5
Name.com - 3
1and1.com - 1
NameCheap.com - 9 (Best I have ever used, about 20 I have used)(Phone support would add +1)
Networksolutions.com - 4
Domain.com - 5

GoDaddy.com - 10 to Premium Account Manager and Joe who is participating in aftermarket fees - related thread; 1 for regular customer service (only trained to copy-paste answers from their screen AND are likely specifically instructed NOT to acknowledge any types of issues or problems @ GD end)

Sedo.com - 8 (may be slow), but professional

Moniker.com - thanks goodness, we do not have any more domains with them

Netsol/RegisterCom - BIG ZERO

Pheenix.com - 10

Fabulous.com - 10

Uniregistry - 9 (there is still a space to improve, such as fixing an obvious bug happening with domain management in specific rare circumstances - reported a few weeks ago, still not fixed...)

GoDaddy - 4 - I had some terrible customer service issues with them.
NameCheap - 8 - would be 9 if site was a little easier to navigate, 10 if they had DNSSEC gui (currently you have to file support ticket to get DS records added to parent TLD for signing). Their customer service rocks.

I don't have enough experience with the others to be fair.