First off, I'm no HT expert, so anyone who is going to take anything away for reading my post will most likely be a 1st timer to HT like myself.
I work at Best Buy. We carry mainly 3 types of cables, from least to most expensive: Recotton, Acoustic Research, and Monster. Using my staff discount, as well as borrow 'open box' items, I was able to judge performance similarities/differences in various brands of cables.
I have tried them all (Recotton for stereo LR audio cables only) and have reached a more educated perspective based on trial, rather than word of mouth.
My initial impression was that Monster Standard cables would be clearly superior to AR because not only are they THX certified, but also almost 2x as expensive.
I was able to speak to my manager and borrow a few open box Monster cables that we had stored under the tills. Here are the cables used for this test:
Monster Ultra Fiber Optics (4 feet)
Monster Standard Fiber Optics (4 feet)
Monster Standard Digital Coax (4 feet)
Monster V3 component (6.6 feet)
AR Fiber Optics (6 feet)
AR Digital Coax (6 feet)
AR component video (6 feet)
Using both Digital Coax and Fiber Optics, I could find nothing that stands out. Even using the Ultra, I could discern no audible difference in sound.

My DVD player is a Denon 1910, while no juggernaut, it's not too shabby. I then switched to my Free-to-air Sat box using the Digital Coax, I could notice no difference in audio.
There was a slight difference in component video between Monster and AR. Monster has a tad more realistic skin tones, and the color seemed a touch more realistic. I used the Picture-in-picture views to compare the two cables. However, the AR cable retails for $39,99, whereas the Monster V3 retails for $139,99. Is it worth $100 more? Had I not done PIP, I wouldn't have noticed a thing either on DVD or Sat box.
In terms of construction and ease of use, Monster irritated me! First off, the video 3 component cables have some retarded twist-lock system that is really unnecessary. I've never found component cables to 'come off' on their own. I almost broke off the output jacks on my Denon 1910 trying to get those cables off. It's stupid and isn't user friendly at all.
Both brands uses gold connectors. The digital coax on the Monster loosened slightly when I was trying to pull it out of my DVD player. That's not good. It seems the glue (or whatever they use) to hold the plastic and the gold connector was not strong enough. No problems with AR. They all semed consistent during connections.
Next, the plastic used for the RCA jack covering is miles ahead on the AR cables than on the Monster Standard cables. It's a softer, more robust plastic than the hard - which feels hollow inside - plastic Monster uses. The Ultra plastic was of higher quality, but it had better be for the price.
The cool thing about the AR cables was the nice texturized rubber grip found on all the cables. It makes it so much easier for users to know where to hold on the cables when inserting in or out. After trying out as many cables as I had, with sweaty hands, I cannot express the practicality of AR including such a nifty, functional part to their budget cables line. Monster standard has 4 cutout indents for gripping which really doesn't do much IMO. The ultra series has a rubberized grip at the base, while good is not on the same level as the AR grip.
Another thing to note is, that the Monster cables' moulded plastic grips are thicker in size to AR. This could be a nuissance on Harman Kardon receivers, or any av equipment where where the Component, Optical or digital inputs are right next to each other. You'd have to shave the sides of the plastic grips to get them to fit.
In terms of the actual cables themselves, AR has a very flexible, soft, outer jacket, which really surprised me. It is REALLY soft to the touch and feels 'more expensive' than it really is. Monster's cable was no slouch either, while not as flexible as AR it is still beefy and nice. The Monster Ultra mesh jacket on the Fiber Optic cable was very stiff and I had a hard time getting it to lay flat. It might be shielded better but I didn't appreciate its stiffness.
Whew! That ws longer than I intened to write. To me, based on what I observed, Acoustic Research Performance Series cables is clearly the winner here. It far exceeded my expectations an a N00B HT user. Also, I happen to like the all-midnight blue look of these cables as an added bonus.

At work I'm pushed to sell Monster, which is going to be extremely difficult for me now, because I cannot recommend them without a guilty conscience over AR.
I'd like to thank you for taking the time to read this, whether it helped you make a choice or not.