I've used and sold AHS, Fidelity, and First American over the last few years.  It's like comparing Exxon-Mobil to Shell to Chevron.  They all offer the same basic product (gasoline), they all put stuff in their gas to make it clean your engine or boost performance (Techron, V-Power, etc.), but at the end of the day, you're buying essentially the same product at about the same cost.

What matters is the service.  Will your rep move heaven and earth to fix your client's problems?

I use Home Security of America (HSA) ... have been using them for 27 years and have never had a buyer or seller complain.  Can't say they are the best, because I can't compare to others that might be out there.  But from my experience HSA has my vote!

I have my own policy with Choice Home Warranty and have been very pleased with them. I also recommend it to my clients. Price is also good.

Unfortunately they have a degree of "suck" based on experience. I use AHS, but I have had problems with them too - some of their service providers are unprofessional is my complaint.

The home warranty company that we use is based in San Jose, Ca. I do not believe that the can help you in Maryland.

The agencies I have been affiliated with have been promoting American Home Shield. Most of my buyers and sellers opt not to purchase

I used to use Choice but, my clients began complaining about their customer service and the fact that they are covering VERY little during the past 2 years. 

So, I (and my clients) have moved on to Cinch. So far, so good!

AHS is who we use, nothing to compare

I believe this is a regional thing. My customer service rep is amazing. She goes over and above serving my client's claims. 

Agreed on the quality approach and not the money-cost

I refer one that is based in Utah, Equity Home Warranty. It has been the best by far and I have one on our property. Do some research on what will serve your clients well, Mike. 

I hate them all. LOL
I have had most of them (for my residence and investment properties).

I have fired them all at one time or the other.

I fired one, then took them back, then fired them again! 

I have been in class action suit with one.

Right now, Choice is one of the 2 I have (fired Fidelity 2x and bashed them silly on their FB site, BBB and elsewhere but they want to CHARGE ME to cancel them so the clock ticks. My rep helped fix a problem right before she retired, for which I thank her)
I would die before I would use AHS (the class action suit) or Landmark who charges an arm and leg and their CS people do not listen.

The other one that is decent in terms of service and offers some 13 month and 2 year is CRES. 

Choice overall is the 'one our clients don't complain about' (YET) the most so far.

First American Home Warranty CRES Plan

Amazon now has a home warranty that I have mentioned to buyers but never used.

Like others have said, at one time or another, they all have issues.  I usually use AHS and recommend to clients, and have had less complaints than others.

The answer is short: None. I do not recommend any since i heard too many complains and disappointment. 

As I posted in my comment: 

Few of my recent buyers who needed help during their first year got rejections from H.W. for preexisting conditions. Even AHSW states: 

'' you’ll get coverage for:

Ryan Huggins - Thousand Oaks, CA sums it up well. Read the fine print for the differences.

I suspect this is a regional issue but I have had a number of homeowners with First American who were very satisfied with their service.