Online is more convenient. There are different limits for folks to play, more games that you won't find at a brick and mortar
casinos unless you're in like Vegas and when you're done you just turn off your computer instead of driving home and that in itself could be an ordeal if you live a few hours away or live near some crowded areas known for traffic.
But for deciding if its harder or not, you would need to know how to identify the type of players at a table either online or live and see how your game would stack up against them. Online, .01/.02 cents is the entry but I've seen tables where player to the flop stats were around 20% so that's usually a tight solid table so you could assume they at least know starting
hands.
At the casino the entry game for NL Holdem is $1/2 you'll find recreational players playing very bad at some tables but sometimes you'll find folks that can play and just want a win their buy in of $200/300 for the day and then head home and they aren't to be trifled with.
So, I wouldn't use generalization but actually find out what you're getting into by working on table selection skills either online or live. Oh and if you don't like the table you're at (ie folks aren't talking/enjoying themselves, are actually paying attention to what's going on, folding a lot meaning they actually have a clue) or see them taking notes on hands then you might want to tell the dealer or the floor person walking around to find another seat since that table might not be so soft for you even at the entry live table.
So I would say to pay more attention to the quality of the folks at the tables rather than the limits you're playing at either live or online.
