I'll start. I voted that live is harder than online. I play about 65% live.
OK, I think they are actually pretty close in difficulty, however I think a few key factors "tip" the scale to make live just a bit harder.
1) No poker tracker/ HUD/ Stats at the ready. you have to collect that data all by yourself, store it, and then recall it and apply it when you need to.
. You might be giving them off. You need to try and pick up tells on other players because they are trying to do it to you.
It is entirely possible that #1 and #2 cancel each other out....but I find my HUD stats to be so much more useful than my ability to pick up live tells...so for me online is easier in this respect.
#3 serious player or not, everybody is stuck watching 1 table. so at least on a subconscious level every player, even the fish has seen how you play.
#4 because of the increased rake and tip it is much harder to "beat" live poker. So, in essence players who manage to sustain a win rate MAY possess additional skills beyond an online player who can beat the same limit.
edit to add: I can't wait for Duggs to reply! We like to have a friendly forum battle/debate every couple of weeks!