I goofed and voted TS/H. But I'd say all are DANGEROUS and DEADLY. Heck, I'm sure more people have died from heat stroke lately than from the other weather phenomena combined.
As for most DAMAGING and potentially deadly, I'd say a single hurricane can do more damage than any other singular weather event, IMO. Like David said, tropical storms and hurricanes have associated lightning and heavy rains, as well as high winds, surge, and flooding. Heck, just look what Allison did.

A tornado usually lasts for less than an hour and rips up one narrow path of destruction, whereas a hurricane is usually much broader. Blizzards and heat can stifle normal daily activities and can cause some damage, but nowhere near the wet, muddy mess of a hurricane surge and associated flooding. Floods are destructive too and happen more often than TS/H's. But factoring in the winds would make hurricane surge/flooding more dangerous.
As for hail -- somehow, as many times as I've been caught in a rainstorm, I've never once been outside during hail and I've only seen it a couple of times on the ground after the rain subsided. I can't imagine it being all that bad, but I'm sure an umbrella wouldn't prevent someone from being bopped on the noggin by a hail thingy every once in a blue moon.
Hail thingy? Seriously, what is one thingy of hail? I've heard of golfball-sized hail, pea-sized hail, marble-sized hail, and even grapefruit-sized hail. So if it's "hail" like "rain" or "snow" when it's a bunch of it, what is it when it's singular? We have a snowflake or a raindrop. A hail ball? A hail drop? A hail bop? No wait...that's a cult.
I suppose the standard "piece" of hail makes sense. But it's so boring.
