There is no substitute for shadowing experience. If you can lay the groundwork now, no matter which road you take and no matter how rough it gets, you will have the rock-solid knowledge that you chose the best possible path. There are too many variables to really account for, but some of the big ones are time spent in school, debt load, intensity of day-to-day studies, geographic location, which specialty/ specialties you end up working in, practice setting... it goes on.
At this point the dilemma probably feels pretty binary: either this OR that. But as you spend time shadowing MDs and PAs, you might find that you like certain aspects of one career over another, but only in certain contexts. It's a complicated thing, and it's worth digging a little deeper before you commit to one path or another.
Remember that PA school pre-reqs are not the same as 4-year med school pre-reqs, and even a licensed PA can't get advanced standing if he/she wants to go back and do an MD program. Likewise, an MD who for some reason wanted to be a PA would have to do the entire PA program like everyone else.
So figure out what you want to do in medicine, where you think you'd be most happy doing it, and which approach or practice philopsophy feels like the right one for you. Only when you know that kind of thing does the choice seem fairly clear.
I chose PA, and 5/8 of the way through school I'm still glad I did. I was able to boil it down to "I want to be a PA because ____," and just as importantly I was able to say "I don't want to be an MD or DO because _____." The actual reasons should be yours alone, but you need to be secure in your answers to both the "why" and "why not" questions. Good luck to you.