Best way to A/B speakers......

blindjim method is seconded. A lot of work but absent a double blind process it is the best you can do at home.

With all due respect, you have just come upon the leading edge of a very steep learning curve. The reason you can't tell the differences is because you have not established a frame of reference.

To use the automobile analogy, On Monday you drive a Porche, on Tuesday you drive a Mercedes, on Wednesday you drive a Cadillac, on Thursday you drive a Mazda. You (probably) can easily retain knowledge of these experiences even though the cars are different in most all respects and demos are days apart. You not only retain the experience of the individual performances and the differences between them but you assign a value to them.

Probably not so with audio. You probably have never heard what a good system sounds like in an audiophile's home and/or you have never visited a dealer show room where time an effort has been expended to proper set up a system. Most dealers who are trying to sell good speakers will not use an A/B switcher because each speaker has seperate needs to sound good, including selection of the amplifier, as well as room set up. So, in that respect you have no goal. With out such a frame of reference, you could go into a store which utilizes a speaker switcher like your car audio store, hear two terrible speakers, and buy the best and assume you had good speakers. You could hear a very good speaker not properly set up and driven and it could sound like crap.

There is no quick fix for this problem. What I would do is get the assistance of some audiophiles in selecting a system which will sound the way you think you want it to sound (by telling them what aspects of sound are important to you in response to thier questions) and setting a budget to work in. DON'T just go into a store an buy the best speakers (according to your ears) that you can afford and take them home and expect them to sound great. It ain't going to happen unless you have a habbit of winning lotteries.

FWIW.

Thanks for the responses guys. I could never buy a pair of speakers based on store listening as I need to be in the comfort of my own home without pressure or time constraints, even then it doesn't take hours - it takes me days to fall into a good listening groove.
I bought the Dali Ikon 7s along with the Nait Naim 5i and Cambridge 840c (CD player) using Kimber 8tc and Hero ICs) based on some top reviewer's ideal system under $5000 in TAS. The system was great - my first step into higher end audio. I then bought the Magnepan 1.6, hooked them into this system and thought "what is the big deal." I still preferred the Dalis but after about 10 hours of listening to the Maggies I got it and I can't listen t the Dalis any more. This has me wanting to switch the speakers about quickly to really put a finger on what I like/don't like.
Now I have an expensive system hooked up to the Dalis - a Pass Labs X250.5 with a Parasound JC2 and good cables......I think the $1.500 Naim sounds better!!! I know when I hook up the Maggies that this gear it will be very nice sounding as the Maggies do need a lot of power but it would be nice to switch back and forth immediately.
I think my strategy for buying speakers in the future, since being objective in a given timeframe can be difficult, is to read up as much as I can on reviews, narrow this all down to probably a few classics and understand their sound from many peoples perspectives and accept that hundreds of thousands of people can't be wrong in the case of certain speakers (Maggies, Vandersteens etc).

Thomas, What ever you do don't underestimate the impact of properly setting up speakers in your room. A long and often tedious task. You mention Dali's and Maggies. I can't imagine two speaker types with more obvious differences in set up and amplyfing requiremnets. Proper attention to set up an room acoustics can get some excellent sound from speakers that some might consider uninteresting. FWIW.

An alternate method would be to set up identical systems in two different identical rooms, the only difference being the speakers.

Once set up and playing, you just run back and forth between the two rooms listening in each room for around 30 seconds at a time.

This way you're sure to be comparing crab apples to crab apples. And it's also a great way to get into shape!