what cartridge you recommend?

Most likely you will need to adjust VTA on your RB303. I use Acoustic Signature Rega Spacers with great results:

Adjusting the height of your Rega tonearm is easy with Acoustic Signature's Spacer Set made from Stainless Steel.

It allows you to adjust the height from 0.5mm to 3.5mm in precise steps of 0.5mm - without removing the tone arm.

Loosen the screws, insert the spacer(s), lock the screws back down, and your tonearm is ready to play.

The set goes for $95.00

Happy listening!

Thank you for your invitation to your forums.
I am very pleased that you reply about adjustment VTA and arm height.
I intend to purchase the Rega spacer, and to adjust it.
Thank you very much for your advice.

P.S
Though I have heard that sound quality deteriorates when I use a spacer on Raga Arm, is it true?

sound quality deteriourates just about from anything, but proper set-up suppose to improve it. that's why there are spacers for proper VTA.

Thank you Czarivey!
I'm following you,,,