Ah yea, the elbow strike. One of my favourite moves to use...
Ahem, anyway here are some differences:
1) The elbow strike is stronger in power than the fist.
2) The elbow bone is harder than the knuckles/fist.
3) Elbow strikes are shorter distance than the fist and therefore are good for close range. At close range, the elbow can reach full distance much better than let's say, a jab, which uses a fist.
4) Elbows can be used as leg breakers. Yep, serious here. If someone fires a high kick on you or jump kick, let's say a hook kick of roundhouse preferably, just charge forward and elbow strike their shin or the back of their shin (depending on which kick they used). I tried this before, it works and it gives them a nice amount of pain and damage, maybe even crack their leg. Also, since your elbow bone is hard, it'll take quite a lot of power from a kick to even phase your elbow on contact, seriously.
Well that is the pros elbows got over fists, anyway, here's the pros fist got over elbows:
1) Longer range, can keep off your enemy.
2) You can use more attacks. You got a jab, crosses, backfists, etc. Elbows can use some of them, but the time difference is at least more than 6 times, at least imo.
3) The fist has a wider range of the enemy's body to hit. Way more places to hit. Elbow strikes can probably hit the neck upward level. Fists can go all the way down to the stomach.
4) The fist can change to other positions for the right situation. If you need to foreknuckle someone in the eye, change it. If you need to spearhand their throat, change it.
Really, in the end, both elbow and the fist are equal. Nearly all body parts are equal. You need your head to think, your legs for kicking and large damage power. You need your elbows for damage, fist for range and diversity, they're all equal. These SD guys aren't thinking properly to see the beauty of the fist and how both of them are just as good.
Now in summary, it just comes to your choice. What do you think is better for you? Power and toughness, or speed and diversity/range?
That's all from me, lol. Hope this helps.