I always stay in the Epcot resort area. Whether or not the Poly is closer, I'd much rather walk through the lovely World Showcase in the morning than take the crowded monorail. I also think the Beach Club is a beautiful resort.
Yes, the monorail puts you at the front of Epcot, but you still have to get TO Epcot, as well as have much longer bag check and ticket lines to go through.
**ETA that 5 resorts utilize the International Gateway entrance to Epcot, whereas 16 WDW resorts (including the campground), plus everyone staying off site enter through the front gates of Epcot.
If you take the monorail from the Poly, you stop at the GF, the MK, and the Contemporary before changing to the Epcot monorail at the TTC. If you walk to the TTC, the walk takes about as long as walking from the Beach Club to the International Gateway entrance of Epcot.