Dumbbells.

Kettlebell.

There’s an interesting discussion on the Dragon Door forums on the merits of dumbbells vs kettlebells. For anyone considering the purchase of their first kettlebell, some of the differences noted were :

• kettlebells have their centre of balance off-centre, which offers the stabiliser muscle benefits usually associated with odd-object lifting
• performing swings, snatches and cleans feels more natural and fun with kettlebells
• From Pavel Tsatsouline :
  

  the ability to do many swings safely with a KB. With a large enough DB you would take your knees out with a pronated grip. With a semi-supinated grip your elbow could not handle the volume.

• kettlebells afford a more comfortable rack position, increasing ROM in presses and making exercises such as Front Squats a little easier

I’d add the following :

• kettlebells have a thick, curved handle; ensuring a great grip workout every session

Not to mention the fact that throwing a large chunk of iron around is just downright fun.