Jelco SA-750D or Rega RB250

I have mounted both on my Sl1200mk3 with custom armboards.  Yes, the Jelco just looks and feels like a better made product.  It tracks well and works great with MC carts.  I love mine.  The RB250 is not very adjustable, mounting and aligning is more of a PITA but with right cart, it sounds fantastic, even with the stock cable. Something like a 2m blue or older Shure carts that I have.  So, it all depends on the carts you want to use really.  
Btw, replacing the Jelco mounting collar is a must.  If you tighten the set screw on the stock collar, the arm pillar will tilt and the stylus will not follow your desired alignment arc no matter what!  Easy to spot by placing a spirit level on top of the fluid reservoir cap.

Jelco 750D easily. You need to go 2 level higher in Rega chain to get the Jelco standard of sonics

@invictus005 What is your cartridge and turntable? Not sure how anyone can recommend a tonearm like that. If you’re looking for inexpensive tonearm with superb build quality (vta on the fly etc) check for vintage Victor 7045 in perfect condition (under $600) and ingnore modern Rega and Jelco. This Victor 7045 tonearm is amazing and easy to use (one of my favorite). Jelco is for MC cartridges and higher mass btw. Rega is the ugliest tonearm ever made (imo) !

The "key words" you have mentioned are all about the cartridge first. I would ingone the MC cartridges (just a waste of money). The Victor 7045 tonearm with decent MM cartridge (like Victor X1, X1II or AT-ML170) simply killing most of the MCs.

Don’t be too worried about the Jelco collar comment. While I agree it is a good idea, it is not necessary. I run a Decca cartridge in mine and there are no tracking issues.

noromance is right! I've been using the 750 for a few years and never changed out the collar and yes I've known about the tweak for a long time.