Although I generally prefer the sound of Maggies to MLs when it comes to the models that are available used in your price range, I will point out that in a tightly-spaced HT setup, the curved panel design of the MLs may be preferrable for it's wider-angle listening window. I'm not convinced that dipole radiators are a good idea in smaller rooms (though yours might not be too small, depending on the layout and setup), and the answer to your placement-sensitivity question is yes, panel speakers can be more prone to response anomolies than box speakers if not optimally positioned. Additionally, you will need to satisfy yourself that a small panel speaker won't limit you too much dynamically if you like to run loud, and that your amplification is up to the task of driving either a relatively insensitive load (Maggie), or a high-capacitance, low-impedance load (ML), both of which can be more demanding and less forgiving than an average dynamic coil box speaker load.
Maggies or Martin Logans?
I think it is time to upgrade again and I am thinking about going with electrostatics. I don't know much about them other than I fell in love with a pair of Martin Logans at a local shop. My room is somewhat small (16' x 18') and I have 2 NHT 1259 home built subs so I am not concerned with low end. I would like to stay under $1200. Does anyone have a suggestion on what speakers would fit in my room and sound good? Is placement as critical as I have heard from others (more critical than regular tower speakers)? They will be used as mains in both two channel and HT. Thanks for the suggestions.