There have been other threads on this subject but I will try again.
I have owned four pairs of Magneplanars including Tympani IVa's (my latest) and also Martin Logan SL-3s. Both companies make interesting speakers that are fun to own.
In general, I have found Magneplanars more musical -- there is something really uncanny about the presence of a good ribbon. (Which also explains the amazing midrange of the Apogees.) However, Maggies require lots of power to perform at their best, they can be tricky to place and they need a bit of volume to open up and sound alive.
Martin Logans on the other hand, have much more resolution at lower volumes. They are easier to place, although the integration of the woofer with the panel is not as seamless as they suggest. If your tastes lean more towards Led Zeppelin than Bach, I would lean towards the ML's. Ditto if most of your listening is at low volumes.
But if you are willing to allocate the space, put in the amplification and time involved in tweaking them to perfection, there is something magical about Magneplanars that is hard to beat.
