Best Arm for Raven One?

Haven't used an Ortofon arm in ages but I agree with Audiofeil. The current versions of Dynavector, Phantom and TriPlanar are in quite a different league, especially with a revealing cartridge like the Atmos.

The other arms you mentioned are not in that league either. Some of them aren't even close.

SME IV or V probably come closest, but IME with several cartridges they lack transparency to low level detail and harmonics (at which ZYX's excel), they lack effective VTA/SRA adjustment, some lack azimuth adustment and their inability to adjust offset angle at the headshell inhibits true optimization of cartridge/arm/table alignment. SME's are beautifully made, solid and easy to use, but the first three arms you listed will allow an Atmos to show you more of what it's capable of.

I believe the cost for the parts to upgrade from a Raven One to a Raven Two (armboard, motor housing) is $1500.00.

My advise is this
http://www.thomas-schick.com/arm01.htm

Raven 10.5

Just as an aside, Thomas Woschick, the designer of the TW Akustic line, used the Ortofon arm as his demo arm until he recently designed his own arm. Do I believe the Ortofon arm is as good as the Phantom? No. But the Raven's own designer may have felt that there was some synergy betweeen it and his own turntable(s).