Thanks to all of you for your responses to the poll and he commentary. Based on the little poll, 3:1 forest is a clearer choice. My takeaway is to boost the time factor / urgency to make the swamp a stronger option and an overall tougher choice. I can make the swamp more certain and the forest less certain time wise. For example, the swamp could be a solid 2 days. The forest could be 5, and that is if you can find a way across the river. (And, oh by the way, there is a way across the river). Any other suggestions on how make this a good party discussion?
Make sure the differences are clear, but ensure that the players have good reason to question traveling through the swamp. Maybe increase the attack rate after you lower the travel time, so: 2 days, 70% chance of attack v. Forest @ 5 days w/30% chance of attack. Conversely, provide good reason that a wide, slow river
could be dangerous, such as if there is a *insert season* rain or substantial winter snow. The Swamp provides high attack uncertainty, but quick travel time, while the forest provides longer travel time, but more "river crossing" uncertainty, as opposed to the pervasive "hard to find path" and "lots of fog" of the swamp, which once solved are solved throughout the length of the swamp, while the river presents variable danger. It could be a dry season, 2 feet deep and easily crossed. It could be a heavy winter and a wet spring leading to high, raging waters.
It's also worth presenting a rough idea of what sorts of combats they might encounter in the swamp or the forest. Undead, black dragons, etc... vs wolves or bandits. I would personally set the swamp danger to a medium-high level of danger, but the forest would have a much more random level of danger, ranging from simple bandits to ogres and green dragons or mischievous pixies. IE: the swamp danger is severe, but predictable, you could preemptively arm yourself against the dangers and be safe no matter what you find. The forest however would be more unpredictable and preemptive measures less reliable.
In addition, if the players are leaving from a town, there may be vendors selling "supplies" depending on which route you take. Because of the above-mentioned ability to prepare or not, one of these vendors might seem more trustworthy than the other. IE: because the swamp is predictable, people who buy from Crazy Gypsy had more success in the swamp because her products are more in line with the dangers, but she charges a higher price for them. On the other hand, Wizened Elf Guy sells a wide range of things that
might help with the forest, but as the danger is more random, people express less use for it, even though his prices are lower.