I have been in love with my Janome sewing machine and my New Homes Serger for years! I would stay with something that has proven to be a good brand for you in the past. I would also consider, at the top of the list, how close you are to the dealer. This is so important.

Another straight-stitch fan
 

Like the other posters who have enthused about the Brother 1500SL, I am a huge fan of my straight-stitch only machine as a compliment to my other computerized machines. I have the Juki TL-18 QVP, also known as the Haruka, and I really cannot get enough of sewing on it. It is fundamentally mechanical, but with the addition of needle up/down and auto thread cutting. On the Juki, I can use the heel of my foot pedal to activate the thread cutter which I love because I have better things to do with my hands that feel around for the thread cutter button.
It really cannot be beat for efficient piecing and it is the best home machine a I have used for FMQ. If you have a serviceable machine with zig zag capabilities already (and it seems that you do and then some) a semi-industrial machine like the Brother, one the Juki TL series machines or the Baby Lock Accomplish would be a lovely foil for the serious quilter.