I had both in the house. Returned the Arcam because I couldnt stand it.
It had enormous soundstage, great bass, fantastic detail, yet.....no musicality. Vague, I know, but it started to irritate me very quickly and I never ever could really enjoy the music. Then I bought myself another rega planet which I could just about stand; small soundstage, grayish sound, rolled off treble, muffled sound, but musical. Eventually, a year ago I switched to the Apollo and have been in audioheaven ever since. For the very first time since I bought my first CDP 20 years ago I now can really enjoy music through CDs. It doesi t all, soundstage, detail, bass (far better then the planet in my system), but above all, real musicality!
I know it's me, I seem to be allergic to high freq distortion or so, strange thing is, there are some DAPs I can really enjoy, especially Sony's (but not Ipods and Irivers, can't stand their sound, neither did I like sony PCDPs).
Anyway, in my book the Apollo is fantastic.
If you go into a shop and do a quick demo it's probable that you'll be more impressed by the Arcam, more highs, more bass, bigger soundstage, more details.
But you buy a CDP to enjoy music, not to hear every detail (I hope).
Take your time, take care to relax, do a careful comparison, see what you enjoy more, I know I would chose.