ill throw my 2 cents in.. I shoot with both.. However I always end up going back to Red for the workflow. I love Red Cine-X and the Red workflow. Also Red One MX footage can play on my laptop and Blackmagic raw can not.. There is a place for both of course. it all depends on your needs. If you can live with the slow boot times and weight the Red One MX is excellent and still yields incredible results..

Now the pros of the BM 4.6k.. I do like shooting the Pro res format in camera and am able to use it quickly and great for run and gun.. I have tried to give up my old Red a few times. But have been unable to. It has paid for itself so many times over it is crazy..

If you have under a 5k budget I would go with he BM 4.6k for a few reasons.. The Red boots slow. is not covered under warranty like a New BM 4.6k would be and is cheaper to have a complete kit ready to shoot. without the need for a lot more accessories.
I think you will be happy with either but it is 10 year newer technology and will probably give you longer use then the Red.. The Red workflow is incredible. And if you want to get into it today. I would recommend a Red Raven or a good used Epic.. if You can afford it. But back to my $5k budget.. Get the BM. Then make some money and buy a Red Raven or better.