both for a great amount of fun!
also Dark Retribution (the one from the DLC) is kinda OP in jelly king.

If I was to point at one specific shard bomb as "the best", it would have to be Shocking Salt Bomb. It does shock, which is really useful against anything but quicksilvers. It's the best weapon you could get against gremlin Ghostmane Stalkers, as it will topple them over as well as keep them from running at all.

But shard bombs don't work like that. There's no one best shard bomb, you need three (or deadly shard bomb but that's really not worth it). That means Deadly Crystal Bomb and then Sun/Splinter and Dark/Salt. It's a bit up to personal preference. If you already have +4 damage or greater, you could go for Splinter but anything below that Sun is pretty much mandatory.

As for tactics, check out my previous posts on the subject:
http://forums.spiralknights.com/en/node/77272#comment-676347
http://forums.spiralknights.com/en/node/69015

I'm pretty sure I've talked a lot more about shard bombs than in those two topics, but they're all I could find for some reason.

In addition, use shield bash liberally; it's great for gathering enemies into tight clusters optimal for shard bombing. Shield bash enemies together and dodge out of the cluster to avoid getting hit. Then apply bombs. Here are also some educational videos on the subject:

Shardbombing with a bomber partner in FSC
Solobombing Snarbolax
Solobombing fiends and Arkus
Rocket puppy room in FSC with shard bombs

For Royal Jelly, I wouldn't recommend Venom Veiler any longer. It used to be pretty much mandatory before the king was severely nerfed, but these days you can just kill him to death with other weapons. Shocking Salt is pretty nice for it. Ash of Agni, on the other hand, will make a breeze out of every encounter on the way to him.