HS will have the two new Star Wars attractions, the two newest Toy Story Land attractions, and Mickey & Minnie's Runaway Railway. These rides combined with Rock 'n' Roller Coaster and Tower of Terror will give you lots of thrilling rides and newer attractions compared to Epcot.
Any food festival easily makes Epcot a full day park for me personally. Future World is a bit of a mess right now with the sea of construction walls. We spent the full day in Epcot in August and had plenty to do (and eat). I'm guessing Monday crowds won't be so bad for the festival. I hear it tends to get busier in the evenings and on weekends, so if you visit the festival early you shouldn't experience crazy crowds.
I've heard that crowds feel bigger at HS simply because the thoroughfares are so small, and the park itself is so small. Epcot has nice, wide paths and more real estate so even if both parks have the same amount of people, I think Epcot will generally feel less crowded.
If it were me, I would choose HS only because we skipped it on our last trip and really want to try some of the newer attractions.
Good luck, and HAVE FUN!