If I had my choice of purchasing an Electro Voice RE20, Sennheiser MD421, or Shure SM7 (the dynamic standards of the industry), and with what I know now (after being in radio for 36 years), I would probably go with the SM7. But I would make sure to go with the original design pop filter of the SM7, which was the slimmer thinner foam, as compared to the larger football type we now see in most pictures of this mic. If you can't purchase it with the slimmer foam, Shure still makes it as a replacement part (Shure part # RK345). If you've never experimented, you may not realize how drastically different a mic can sound by how much foam you add to the front of it. Placing a thick foam pop filter on your mic will drastically reduce those upper frequencies. One of my production guys loves the SM7's, without any foam, but instead with a round gooseneck type pop filter in front of them. The SM7 also has this to die for silky smooth upper end, which is hard to fake with a mic processor, using any other mic. The high frequency SM7 output just sounds so natural and authentic. You just can go wrong buying an SM7. Plus, the SM7 is self contained, so you don't need to maintain a for instance, EV309A shock mount (as we all know, those elastic bands dry out and need replacing at some point). All of the SM7 shock mount is self contained in the mic, just like the SM5, to an extent was.
If you really had some bad acoustics, or lots of leakage from outside the studio (cheap doors, air conditioning noise, etc.), you might consider the Sennheiser MD441. That mic is considered a super-cardioid, where the others that were mentioned above are all cardioids. However, what I've found when using the MD441 in an on-air environment is that it's looks can be a bit deceiving, and the air talent may have the urge to talk off axis into the side of this mic. That will sound awful with this mic, as it is not designed for off axis work. The other dynamics listed above are more forgiving for talking off-axis. So if you used a MD441 for on-air, you would have to instruct your air talent not to talk into the side of it (good luck with that). Looking back, I was never really happy with the sound of the MD441 on the air either. I think that is why we really don't see them out there in the normal broadcast studio that much.
To sum up, I have used, and in some part of my on-air radio experience, have talked into, all of the above mentioned microphones. But if I had to chose between the 4, I would still go with the Shure SM7 (with the slimmer thinner foam pop filter).