I used to be a Meridian dealer and am still and ARC dealer so hopefully I can shed some light on the comparison (exluding the G-series from Meridian).
The ARC CD3mkII is much improved from the MKI, which is still a nice player, but the upgrade is worthwhile. The ARC is livlier and higher resolution than the Meridian 588. The Meridian is more round and friendly by comparison. The CD3mkII is also more dynamic and has tighter control, while the Meridian compresses the dynamics ever so slightly and sounds a bit looser. Some might find the ARC too aggressive, or the Meridian too laid back.
Personally I prefer the ARC. They are both very nice machines.
The ARC CD3mkII is much improved from the MKI, which is still a nice player, but the upgrade is worthwhile. The ARC is livlier and higher resolution than the Meridian 588. The Meridian is more round and friendly by comparison. The CD3mkII is also more dynamic and has tighter control, while the Meridian compresses the dynamics ever so slightly and sounds a bit looser. Some might find the ARC too aggressive, or the Meridian too laid back.
Personally I prefer the ARC. They are both very nice machines.