It really depends on what your front and center speakers are and your sonic preference. If you have B&W's up front or MA's up front you might want to keep a similar sonic signature and buy the same brand series of speakers.
If you listen in a room with the sofa or chairs against the wall, I find I usually prefer directional speakers and not surround bi-poles or di-poles. I have that situation in my upsatirs system where I have 2 pairs of Monitor Audio Gold Reference 10's as the front and surrounds. I love it---great for music and movies. 5.1 surrounds are supposed to be to the side of the seating anyway, so it could be I prefer the directional sound to the more diffused sound.
As far as 2 channel music, if you are listening only out of the front two speakers it makes no difference anyway, unless you engage Prologic II for a matrixed surround. In 5-channel DVD-A or SACD I prefer the directionals. The THX people specify for the surround types you mentioned above.
It is all a matter of taste. I tried the MA Gold Reference surrounds and preferred the sound of having a pair of the same GR 10's that I had in the front. You may be the same, you may not.