Which is the Better Tonearm - Pro-Ject or Rega?

I am sure the OP is not interested in a $1K+ modded arm.  Going back to comparing the Pro-ject and Rega arms, I have used both types.  The Rega is longer and should have lower tracking error.  The Pro-ject antiskate setup is not that great but then you have no VTA adjustment on the Rega unless you buy shims or custom VTA adjusters for extra $.  Both are a pain when it comes to aligning/swapping carts due to fixed headshells.  If you are considering turntables rather than arms alone, the Pro-jects are a better value for the money.  The Rega TTs are a bit pricey for what they are more so if you need to add a speed control box.  Avoid Edwards TT stuff.

Ok, as an engineer, I feel obliged to chime in.  Castings are cheaper than bar or tubing.  Tubing and bar, forged or rolled, have more uniform density than castings. Even if the most advanced casting technics are used, you will still have some internal casting issues, it's the nature of the beast. So maybe Rega uses cast pieces for economic reasons.  Let's not fall for the marketing fluff about castings being more rigid and acoustically inert and all that stuff.  I am willing to bet this claim has never been substantiated. 

Williewonka, that link talks about weldments and welded joints etc.  Please, this is not relevant to the topic at hand.  I design pressure vessels for a living, I know my materials as well as the quality of castings coming out of China (we buy by the boatload).  I am not going to  argue about elementary material science on an audio forum....believe what you must.  I am out.