Tough decision... I read this post a little while ago and have changed my answer about 10 times already.
I think there is a lot to take in to consideration.
Either resort will be great. I have stayed in both and they are pretty much tied in my rankings. Had a great time at both and would be happy to return to either.
I dont know how well your 10 month old travels but as long as they are easy to travel with I think I would go for the 12 nights at POR. (DH would never let me book a trip that long though. We have talked about bringing an infant and his max was 5 days

)
Reasons I would choose WL-
-easy access to MK- I love MK and the boat ride would be very convienent for going back and forth.
If you plan on spending more time at MK than other parks this is a huge plus
(if you spread your time between other parks it really doesn't help since you will have to drive or take a bus to the other parks. I found POR to be very centrally located to the parks)
-Dining options-
what do your dining plans look like? WL is just a boat ride away from great options like Chef Mickeys, Trails End, Hoop de doo, and you already have WCC and Artist Point. You can also hop over to MK easily and dine at those TS places. Although very small Roaring Forks is one of my favorite quick service places in a deluxe resort. Love the waffles with chocolate chips in the morning. MMMMM
-Balcony- will you be heading back to the resort for nap time? If so I would love having a balcony so I wasn't stuck in a dark room while everyone napped. Although I'm not big on spending money for a view I think this would be one time I spend the extra to get a courtyard view.
-Main pool is fun, beach area would be a nice place for your DS to play while your DD hung out in the sand. We also had fun in quiet pool. Very relaxing
-Very close to fort wilderness which has some fun activites for your DS
-Did I mention chocolate chip waffles with whipped cream
Also I don't know your WDW history but I'm assuming this isn't a once in a life time trip so 8 nights is probably plenty if you will be back in a few years.
on the other hand
12 NIGHTS

-POR is absolutely beautiful. It has beautiful grounds and although they now house the royal rooms I always thought POR was a great place for a little boy.
-Main pool is very fun. Cute theme and fun slide. Also have the option to use FQ pool and since you have 12 days you have plenty of time to fully explore POR and FQ
-PORs food court is probably my favorite food court. So many choices and you can hop over to FQ for more variety if needed.
-if you happen to need more dining options DTD is just a quick boat ride away.
-speaking of the boat ride to DTD, you will have plenty of time to take your son to Splitsville for some bowling or to the movie theater if so inclined (DH pretty much insists on hitting the movie on vacation) It might be a good option if one parent stays in the room with DD during naptime and one takes DS to DTD.
-I missed Yeeha Bob, but kids seem to enjoy his show
I guess I'm really no help. Like I said, tough decision. I think if I really had choose and I knew I'd be back in a few years I would pick POR. You will really be able to slow down and go at a relaxed pace.
I think I would save the WL stay for when DD is a few years older and she could fully enjoy being close to FW and MK.
Either option sounds great
