thx Pyrrho.
Hopefully I can post some url's after this post, and I can show u some speakers I had in mind.
http://apollohifi.com.au/products/WHARFEDALE_DIAMOND_10_4_Floorstanding_Speakers-704-0.html
Actually here's those Wharfedales I had in mind.
I have not heard them, so I cannot comment on their sound. Ideally, you will listen to a variety of different speakers, with music with which you are familiar, and of all the types of music that you listen, and then pick the ones you like best. No speaker is perfect, and so it is a question of which virtues you require and which vices you can tolerate. Different people are quite different on these issues, so their opinions (and mine) will have very limited value in your selection.
With a home theater, one typically uses a subwoofer, and so one can often save money (or buy a better line of speaker if one wants better sound) by buying bookshelf sized speakers that do not reproduce the deep bass, which is not a problem because one sends the deep bass to the subwoofer. However, the speaker must still go deep enough in order to not have too high frequencies go to the subwoofer, which would be a problem because one can localize upper bass by sound, and therefore sounds that are supposed to be coming from a particular speaker in the surround system will come from the wrong place and be noticeable. The THX standard for this is 80Hz, and I recommend making sure that the main speakers have a -3dB point below that to ensure that this will not be a problem. In my case, I am using the original U.S. version of these for all channels (except subwoofer, of course):
http://www.kellsieavdesign.com/products/Leisure2SE.htm
It would cost a good deal more for me to have tower speakers in the same line. Of course, I could have gone with a lesser speaker line and gotten tower speakers at that price point.
The main drawback to this approach
typically is that bookshelf speakers usually cannot play as loud as tower speakers of the same line, though that is somewhat compensated for by proper setup and use with a subwoofer; one typically sets the main speakers to "small" and sends the bass below 80Hz (or whatever frequency seems best for the particular speakers in question) to the subwoofer. In the case of my speakers, tower speakers of that line:
http://www.kellsieavdesign.com/products/MG.htm
use the same tweeter and [mid]bass driver, but add an additional woofer for the deep bass, and have the crossover altered to be higher for the tweeter (3.2kHz vs. 3kHz for mine) and at about 150 Hz for the lower woofer, so it could theoretically play louder than my speakers could, because with mine the tweeter is being asked to do more of the frequencies, and the woofer is being asked to do more bass (80Hz to 150Hz). However, my system plays louder than I ever want to hear it, with great clarity, so this is not a problem in my case. But it could matter if I had a much larger room, or were crazy enough to listen at volumes that would do permanent damage to my hearing. And obviously, this is a very specific example; different lines of speakers can play louder than others, and so what one should do when auditioning speakers is to make sure that they can play as loud as you ever will want to hear them. Keep in mind, maximum loudness has nothing whatsoever to do with the quality of the sound, so when one does not have enough to buy what one really wants, one may be faced with a decision between a speaker that does not play quite as loud as one would like or a speaker that does not sound as good, and for that sort of question, you must decide for yourself what you value most in a speaker.
As for whether a speaker is difficult to drive, I recommend looking for the minimum impedance rather than the nominal impedance, as some manufacturers of speakers are essentially lying when they label the nominal impedance of a speaker (there are no precise standards required for the claim of "nominal impedance", and therefore they can say pretty much whatever they want to say). If you can find a professional review in which the speaker has been measured, this can tell help you tell if you need to be concerned about the impedance.
Here is a brief article explaining what impedance is:
http://en.wikipedia.org/wiki/Electrical_characteristics_of_a_dynamic_loudspeaker