I have always used plywood when building shed floors. Obviously T&G will provide a stronger floor. The other factor you need to consider is whether or not the plywood should be pressure treated or not, and I always use pressure treated. Its a little more expensive but well worth the extra expense in the long run.
And, should it be 1/2", 5/8", or 3/4" thick? Here again, the more the better. Don't put down a shed floor that you know you may have to replace in 5 years because it just wouldn't stand up to the weather with moving in mowers, bicycles and the like with water being a heavy duty culprit to decay and rot.
Take the extra precautions.
Go with T&G, pressure treated, and 3/4". Its just a shed, probably not huge, so you're extra expense is going to save you headaches down the road.