in person poker
Personally I do not have much experience with poker at
casinos, I have played a couple of cash games in a casino but low stakes and it went average, folded a QQ with higher kicker than my opponent on a wrong read with a chance of straight on the table and i think there was a chance of flush also, I played a tournament once but not too much people.
In my opinion when you play poker in person it is really hard and is a more
bluff based poker since you have a lot of information from the players reactions that can tell you where you are standing.
When it comes to online poker I have found that the use of the time clock and the size of the bets are pretty much all the information you have regarding your opponent so you have to play a lot more based on the cards you get than on bluffing (still you can bluff a lot) and you do not have to worry about your reactions if you have a great hand or if you are bluffing hard.
However obviously the online player gains a lot more experience in a faster time since he can play significantly more than the average in person player and the online player can also play in multiple tournaments at the same time.
In difficulty I would say that currently based on my experience in person poker but I do not have enough experience in that area in big tournaments to be sure.