That is the Nitronome, Big Angry Bomb, and Irontech Destroyer.
What's the difference among the 3 5* bombs?
Basically,
Charge Time: Nitronome > Irontech > Big Angry Bomb
Blast Damage/Knockback: Big Angry Bomb > Irontech > Nitronome
However, BAB and Irontech slow you down while you're charging them.
Also according to the bombers thread, the charge time difference between them means that Nitronome still does more damage overall, as long as you can place it consistently... and given that it's just a blast bomb with a bigger range, you should definitely be able to place it consistently by the time you get it.
It's pretty much accepted that the Nitronome is the best of the three, and the Big Angry Bomb is more or less a joke weapon as it currently is.
The bombing guide has descriptions of all these bombs, and more :D
http://wiki.spiralknights.com/Bombing_Guide#Nitronome
http://wiki.spiralknights.com/Bombing_Guide#Big_Angry_Bomb
http://wiki.spiralknights.com/Bombing_Guide#Irontech_Destroyer
Big Angry Bomb is a huge radius, but painfully slow charge.
Irontech apparently throws enemies farther. Also a slow charge.
Nitronome is a tiny bit less radius and a tiny bit less knockback, but it charges fast and allows fastish run speeds.
Long story short, make the other two if you're feeling interested. Get the Nitro for your first, like I'm doing.