If your eventual goal is to use your photographs on large posters or billboards then all things being equal, bigger the sensor, the better. On the other hand, one reason 35mm film became so popular when 4x5" film was still the "standard" was you could take a 35mm camera places it wasn't so easy to take a 4x5, and you could get more work done. When you think about it,that trade off still exists today.
So ask yourself what kind of shooting you are likely going to do, and buy accordingly.
The other side of the coin is back in the days of film, I knew a lot of guys who used both large and/or medium format, but still kept a 35 mm handy for those opportune shots. I see the same thing today, guys with big dslr outfits who still carry a smaller sensor camera for those times they cannot lug around the larger camera. You might end up doing the same thing someday, and nothing wrong with that.
One last point, not seldom covered, but regardless of your camera choice, I don,t like buying a new camera when it first comes out. I would like to say wait for six months after a camera comes out, but the odds are,how fast things move, they will have two new models by that time, so you get kinda stuck.
But to give you the example of some recent Nikon models (I shoot Nikon), the D3100 was a vast improvement over the D3000 in many ways, the D5000 was an excellent camera but had serious firmware issues until the D5100 came out, and as much as I would love to buy a new D800, the left focusing issue has me standing back and watching, waiting. Film or digital, nothing worse than having that perfect opportunity to shoot, and then finding out that you have a bad SD card or the film wind crank on your 35mm snaps. Technology changes, Murphy's Law does not. So remember than whatever you buy, research it first for stability.