what are some of best tonearms you own or experience with.

I also vote for the SME V - I use them on both of my tables.  The Grahams are also excellent, and at the lower end some of the Regas give very good value .

I have played around with things like the Mission Mechanic (good luck finding one) which were quite good.

www.designbuildlisten.com/ The Wand Plus 10.3 wrangled onto a 1980's Linn Sondek

Surely 'the best arm' is the one that best suits the cartridge that you are using and the turntable it is mounted on?
  The 'best arm' for a high, medium and low compliance cartridges will be different?
   I've had an SME V, Helius Cylene, Terminator, and RB 600, with various cartridges. I now have an Ikeda CR 407 with and Ikeda 'Kai' mounted on a Merrill Williams 101.2, which is my favourite combination, to date.  

You didn't mention a budget. For $2K and under, Rega makes the best arms for the dollar. It's not even close. RB3000 ($2200), RB880 ($1200), even the BR330 at $600 will outperform ones that are several times the cost. They also have a super expensive one made out of titanium not available for a standalone purchase that comes with their super rare/expensive Naiad that was used as the basis for their high end tables.

Above that, I leave it to the big spenders who patrol AG. I know there is an interesting one for $4K that doesn't touch the plinth from Integrity HiFi in Canada. Only found out about it because I bought a Tru Lift arm lifter from them. They swear it makes any cartridge sound great. Conceptually it makes great sense to have total arm isolation with no motor or platter noise or vibration. Anyone ever try an arm totally separate from the table?

Tru- glider, no bearings sits next to turntable , sold my Schroeder ,not even in the same league