I can't comment on the 3A as I have not heard that one (but I do hear a lot of good things about it)...
As for the Tylers and GMAs, I have heard both of these, and have owned the Signature Monitors (technically I still do, as they are the top half of my Linbrook System two piece floorstanders).
I The GMA Callistos I heard about 3 months back and was quite impressed. They get much lower than one might expect, and they had very nice sounstage depth and detail. Classical music seemed to mesh very well with them in particular, and I could easily be happy with them in my home (save for their looks that just don't do it for me, but did for the other person who auditioned them with me)...
The Linbrooks are warmer speakers than the GMAs and get even lower bass still. Speed of drivers and midrange are both close between the two, but I give the edge to the Linbrooks. Top end is about a draw IMO... I loved them both in that area. Dynamics I would give a slight edge to the Linbrooks...
Bottom line is both speakers are superb and I am sure you would be happy with either of them... If you prefer a bit of a warmer sound then probably the Linbrooks would be a closer fit (but keep in mind they are rear ported, so yo will need some space behind them)... If your tastes are a bit more bright (but not overly so) then the Callistos may be what you are looking for...
---Dave