Seems these threads always lead to someone bashing one or design, then someone else has to jump in and bash something else and then some body starts ranting about something else.....
To the OP,
There are pro's and con's to every design out there. Some may be "Race-Ready" but that really doesn't mean much if you're building a weekend warrior that can still be use for DD duties.
Do you're homework, research here and elsewhere on the WWW, talk to people locally that wheel the same trails that you do.
Long Arms will most certainly provide superior ride quality both on and off road, and yes you'll get a lot more flex than a short arm system. Keep in mind that an un-seated coil may make a great photo-op....but it's not doing anything for you when it really matters. Weight on the wheels is far more important than excessive articulation.
Best of luck with your upgrade! (Regardless of which direction you choose.)