AR-VT-200 vs Vtl MB-450

Both are wonderful but i would go with VAC for best build and sound quality.

VTL service is first rate if you buy from an authorized dealer. If you are buying used in the open market you may encounter problems. 

The 450s are very friendly. That is they fail nicely simply blowing a fuse if a tube goes bad. Check the archives for stories of what ARC amps can do in the same situation. 

The 450s are also very adaptable to suit your speakers due to the adjustable damping factor

By the way do not buy gen 1 450s. They are obsolete and you will encounter maintenance issues. 450ii from a dealer can be brought up to iii but it’s costly (albeit worthwhile). I own the iiis upgraded from ii and they have given years of sterling service 

The ARC VT 200 is not user friendly when it comes time to replace the small signal tubes. They have to be biased. Its not for the novice.

https://forum.audiogon.com/discussions/please-give-me-advice-about-an-arc-vt-200-amp

One other consideration -- VTL will insist you use their tubes. A full set for a MB-450 II or III will cost you north of $1600. Using any one else's tubes you will run into maintenance issues with them (I'm not saying they won't work, just that VTL are fussy in this regard). Of course the II and III have full protection and auto-bias so they are a cinch to use but important you have the heads up on cost of ownership

Finally on the Gen I -- I'm sure it's still a fine amp, but not reflecting the current VTL design philosophy and outside of a trusted dealer relationship not sure about how easy to maintain it will be (although the design is such that I'm sure any competent tech can do it, I've done routine repairs on my amps myself (replacing binding posts I managed to snap off) so they are easy to work with)