I prefer Online for the freedom it provides. I could never earn offline, what I currently earn being online.
I've had both and been pretty successful. Merging the two is IMO the easiest way. Right now I market and sell my online solutions offline where there is much less competition. This allows me to charge more and gives me the interaction that I can't get from sitting at a computer. Online is great for passive income and thats what brought me over. Granted to actually "make money" online it takes a ton of work/time and usually more than an offline business. It's on your own terms and you can work whenever you want though. Online is generally much easier to "start out" compared to a brick and mortar business but to actually make money it takes a lot of work and doesn't start paying off for a while. You could start a hot dog stand and start out making $100 to $200 a day but thats it. Online you could spend a year or two building a business to start making $200+ a day but in the end you're making more, have way more freedom, and you have potential for more income. Either way if your looking for easy money or to get rich quick you need to be really good at something illegal.
I find it easier to make money online, because you can just create turnkey sites and other simple setups of the like. You might not make anywhere near the amount made on your day job, but setting up a website and then letting it ferment sure is easy.
Not sure how you mean "easy" but if I had to pick one I'd have to say online, especially if you're very focused on a specific niche.
Each has it's pro's and con's. I've made more money doing offline work than online. To be successful in either takes a lot of work. Finding business offline and working with people is somewhat easier but there is no room to scale. Online businesses has lots of scale built in but takes a lot of time to be successful at