This is an interesting question. On the Red corner we have hot shoe strobes: they are (relatively) cheap, small and portable and recycle pretty fast, but they need lots of AA batteries. On the Blue corner we have monoblocks; They are big and more cumbersome but they give A LOT of light.
So whats the trade off, when are you better getting several small hot shoe strobes and when are you better off using one big light? This is not a trivial question to answer especially since hot shoe strobes measure in GN, while monoblocks measure in Watt-seconds. now with TTL monoblocks this becomes a really interesting question.
Neil van Niekerk did an empirical test trying to answer that question. His comparison addresses the power aspect while leaving convenience, price, light shape and modularity out, but even at that it gives a good idea about how to begin dealing with the trade offs involved.
Neil conducted two tests, both with a 34m GN Nikon SB910 (set to 50mm zoom) – full power vs. a 500WS Profoto D1 (similar to the TTL enabled 500WS Profoto B1 only with no battery) set to full power as well.
The test shows that the B1 is about 2.7 stops stronger than then the 910.
The 500 WS juice from the Profoto D1 gave us nearly 3 stops difference in output. Actually closer to 2.7 stops judging by the light-meter and the photos
That means that for power, you would have to get about 6-7 hot shoe strobes to match one B1 strobe.
For sheer brute power though, it can’t match a studio-type light. And this is where the Profoto B1 battery powered flash (vendor) shines. True wireless control and with TTL capability, it becomes very easy to use and set up on location.
This also takes us in an interesting direction. It is quite often mentioned that portable studio lights such as the Profoto B1 are quite expensive. But if you break it down into a comparable number of speedlights and wireless transmitters (and possibly battery packs), then the all-speedlight option becomes quite expensive. An interesting consideration
You can read the full comparison over at Neil’s blog.