Akdom, I think the Fiat / Porsche comparison is inaccurate. There is not that big a difference in sound. In spite of the longer history of the SM57, to my ear, the SM57 sounds better on congas than the Sennheiser e604 or the e904, although the Sennheisers are lighter, smaller, more convenient, and cheaper. I think the slaps, both closed, open, sound more natural through the SM57 than either the e604 or e904. I have used all 3. Mic placement is very important and SM57s on mic stands give you much more flexibility if you know what you are doing and experiment a bit. On a quinto or smaller conga, the Sennheisers can get in your way while you are playing and some conga players won't use them. All 3 have a similar cardioid pattern of pickup at 1 kHz. Tonio and Akdom, neither of the Sennheisers or the MD421-II is actually supercardioid or hypercardioid as you are suggesting, all are cardioid. Although the e604 and e904 have a little more lobing and stray pickup at 180 degrees off axis at 125 Hz as well as 2kHz and some higher frequencies, given the direction the mics will be aimed, the close micing, and the relatively high sound level of the congas onstage, this is not a big deal and feedback is not generally a significant problem with conga mics. Frequency response and polar patterns can be seen at the Microphone-Data.com website (you have to register and login).
http://www.microphone-data.com/microphone.asp?mic=424For live use onstage with multiple different percussion instruments like conga, bongo, timbales, and drumset, the SM57 gives much more flexibility. The Oktava MK012 sounds a bit brittle on congas to my ear but can sound really good with a little EQ. It is more of a recording mic and allows you to switch capsules from cardioid to omnidirectional. I have not tried the Sennheisers on bongo. For congas, being attached to the rim can cause the Sennheisers to pick up some of the unwanted sounds, transmitted through the mic mount, of your hands hitting the edge of the drum. Whether this is loud enough to be heard depends on your playing technique and other factors, try recording the sound off the mixer and listen to see. You get some of this effect with the LP Claw, but it is not as loud as with the Sennheisers. On the other hand, mic stands standing on the floor can pick up stray sounds of walking or foot tapping if you don't use a low cut (high pass) filter at 80 or 100 Hz. For your uses on many different percussion instruments, I think the SM57s will give you more flexibility and better sound if you are willing to buy, lug around, set up and takedown all the mic stands. If you want convenience generally limited to congas and toms, try either the Sennheiser e604 or e904. I have not found much difference in sound between those 2 Sennheisers and the e604 is lighter, cheaper, and less "bouncy" on its plastic clip than the e904. The MD421-II is really expensive for live use, and breaks more easily than the other mics, so for those reasons it is more of a recording mic than a live onstage mic.