Based on your "AC/DC, Kiss, Led Zep" list, I'd say 100w, especially for AC/DC. The other two could go either way. However, the differences between 50 and 100 can be somewhat subtle and are found mainly when pushing the amp hard (loud).
In my opinion, the biggest differences have to do with the way they feel when you play, not so much the tone.
Here's how I would describe them but there is some overlap between the two and these are just subjective.
--- 50 ---
smooth
sweet
can be more "forgiving" to play
a little more compressed
feels more "loose" or "bouncy" when hitting chords hard
less clean headroom
--- 100 ---
bold
punchy
feels "tighter" when hitting chords hard
more clean headroom
stronger bass response
In other words, if I wanted to record a "smooth, buttery, soul-moving" blues solo, I'd choose a 50 (actually, I'd use a Marshall 18w, but...). If I wanted to record a "punchy, in-your-face, chest-thumping" AC/DC-like rhythm part, I'd use a 100. How's that for subjective?
You can't go too far wrong with either. It's not like they are totally different and exclusive. Hope this helps.