Both manufactures are 'entry level' by many peoples eyes.
For me, it would be Avenger X tact hands down, because I don't want the action / magazine ect near my face, so I don't do bullpup designs, only carbine, where my cheek can rest a reasonable distance from all that is happening within the internals of the gun.
Especially for bench....however for balance the zelos gets a point.
22.8" barrel on the Avenger
26" barrel on the Zelos
Zelos gets another point there.
Zelos 250cc vs Avenger 210cc (bottled)....zelos wins again.
Avenger max fill 4350 psi vs Zelos max fill 3600 psi, avenger wins / gets point here.
Avenger regulator can be taken to 3000 psi, unsure of zelos, doubt its 3000...so Avenger wins here too.
Plenum volumes on either? IDK, not noted on websites.
Trigger quality? Never shot either, so cannot comment.
Avenger high capacity mag = 16 rounds in .22, and for zelos 20 rounds. Small win for zelos.
Avenger has dual gauges, shows both pressures, zelos does not afaik. Another point of avenger.
So really its subjective, above is just some things that stick out to me, and I would still lean towards the avenger
-Matt