Time travel works...just invented, by you. The tests prove it! Now for the human tests.
It works by poking the residual timey-wimey weebley-woobley stuff just enough for you to move yourself and your time machine to the point specified. For some strange reason, your time machine is restricted to destinations on Earth. Annoying, but that's a feature coming in Time Machine 2.0! Flying is also on the product backlog.
Your significant other works as an epidemiologist and has implored you in the design of your time machine to include a measure that prevents you from bringing back any nasty diseases (their job is hard enough with the current world diseases, thank you very much). You choose to implement this by having the time machine test your vitals and a quick blood test for any signs of infection. If any signs are found, you may not travel to a different time but you may travel to a different location within your current time. This feature may not be overriden because of several layers of interlocks and protection mechanisms that you cannot get around.
You have access to all of 2015 medicine (being with an epidemiologist has its perks) and can take an extensive medical kit with you.
For your first long distance trip, do you go back in time or do you forward in time? Why?
You don't have to worry about the Grandfather Paradox or causality or any of the other nasty time travel problems. Physical security of the time machine itself is also taken care of, so no worries of theft or breaking & entering. This question only addresses the relative medical merits/demerits of doing your explorations before your own time or after your own time.