Jelco SA-750D or Rega RB250

@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.

But which tonearm sounds more welly? Which one has more midbass bloom?

It doesn't work that way. I mean if you stick an AT440MLA on either tonearm, you are not going to get midbass bloom. 

As for the collar, yes the stock one does not cause severe problems and is fine for most people.  However, if you try to print out and use an arc protractor, you cannot trace the arc well because the arm pillar is not vertical.  May or may not be audible to you but what I say can be easily verified.