I've seen all 4.
Heroic Age - Average, a little bit ofa space opera that gets mixed together with a god-like super robot. (Punches through black holes, wipes out planets with a single blow etc.) The character designs are from the SEED guy, but the ship/mech designs are decent.
StrikerS- Below Average/Poor: Mostly for nostalgia. Plot is so-so, but got skewed by too many new characters, some of which didn't need to be included. Also Subaru and Vita are awesome. Signum barely gets any action screentime, neither does Hayate. Arf and (other wolf guy) say nothing (except for maybe one or two lines out of 26 episodes)Pacing could have been better. Mostly for nostalgia/contiuation, lezbots, beamspam and White Devil.
Seirei no Moribito: Very good-Excellent, animation is fluid, story/plot is good. Characters are believable and develop very well. The pacing is relatively slow, but the fight scenes while uncommon and freaking epic. (makes me wish there was more) More of a political intrigue type of anime then anything (something like Twelve Kingdoms MKII for an example) You get your shota and then theres Balsa.
Idolmaster Xenoglossia: Above Average Starts off a bit slow/silly with straightfoward plot (How its introduced is how the story goes) However it picks up quite nicely towards the middle and ends pretty strongly.
My suggestion is go with what you like. Seirei no Moribito is my favorite out of the four because even though it was slow I believe it was well worth it. It might because I'm patient but still.