If you’d made this decision in March (when next season's pass prices were announced and available), you could have skied the rest of this season free on 13-14 passes, an option only available to first-time pass buyers, and only if paid in full at time of purchase. I realize, though, how big a decision this all is...
I know! I wish we had been able to make a decision sooner, but we were wrestling with several options at the time. We did have frequent skier cards so at least we were not paying full price for our ski days. We also did the easy pay plan where you put $50 down and then do installments over the summer which is nice, but wouldn't have allowed for the free spring skiing.
If you are going to choose Sunday River as your home base (and I’d advise that over Loon due to greater acreage), get serious about seasonal rentals pretty soon, so you’ll have some choices. If you go with off-mountain, you’ve got some other decisions to make as well: whether you want to pay for preferred parking, seasonal lockers, etc (ka-ching). On-mountain is nice for location, but be wary of resort condos - construction is - well, not great in many units (i.e., noise). South Ridge town homes are probably the best. Locke Mt is DE-luxe, i.e., mega bucks. Avoid Sunrise, Cascades, Brookside, Whitecap - sub-standard construction and paper-thin walls in these units.
I'm still undecided about this, though leaning towards Sunday River as it is one of our favorite mountains. The pros to us for Loon is it's pretty much exactly 3 hours from our house and all highway driving which is good for inclement weather. We know the mountain really well, love the guys in the tune shop who give us deals all of the time because we are there so much and also have a couple of friends who ski there close to every weekend as they belong to a ski club nearby. The cons are it is a smaller mountain with less variety of terrain, I am wanting to make strides in trees and bumps, but sometimes the trees are barely open in a season and there are almost no bumps, almost all trails are groomed. It also appears more difficult to find a rental that is pet friendly which is a must, and they seem a bit more pricey. Haven't found any up yet that meet our criteria, but many rentals there go through May so I don't think they are geared up yet, I've been told to check back in June. Hard to get out of my comfort zone here though, it's the only place I've skied at alot for the past few seasons then we've jumped around a day here and there at other mountains, so Loon is the most home like mountain I've ever had so I guess I have a soft spot for it! 
Sunday River, like I said is a favorite of ours, has a ton of terrain and variety, and we know how to avoid the crowds there from previous holiday trips. Though more tips are certainly welcome! They also have seasonal ski lesson packages which I'm very interested in whereas Loon really does not for adults unless you form your own group for the season, and I don't know enough people who ski there consistantly to do that economically. The biggest con is it's at least another hour drive for us each way to Sunday River. I have been looking at rentals there already and actually am speaking to one person in particular with a 1 bedroom condo on the access road, it's also on the shuttle route so we wouldn't have to park at the mountain if we didn't want to. We want to go see it in person so I am trying to find some others to go see all on the same weekend so we don't have to drive up a bunch of times. I'd LOVE to get a place on mountain, but the crappy places you mentioned which we only stayed at once before only staying at the Jordan hotel there on subsequent trips are super loud like you said, and not pet friendly for renters only owners. My dog would hate the noise anyway, she'd be barking up a storm so it'd never work out. South Ridge and Locke Mt. do allow pets, but they are super expensive. Locke Mt is out of our price range even for the one 1 bedroom unit I've seen, and South Ridge I've only seen 2 and 3 bedroom places for rent and they are sky high due to that as well like $10,000 for the season is the cheapest I've seen and most are $12,000 and up not including utilities which would also be higher for the larger units.
I've just been searching online and it's hit or miss to finding seasonals. Are you aware of any specific websites or realtors you could recommend for finding seasonal rentals up there that I might be missing?
There are lots of weekend/holiday crowd-avoidance strategies at Sunday River, as it’s a wide, spread-out resort, not unlike Killington. Glad to help if you’d like! I tried one year, many years back, to get a diva get-together going there. Didn’t work out. I have, from time to time, met up with individual divas there and had a good time. I did a lot of skiing at Sunday River my first 3 years here in Maine (of 12).
We tend to like the terrain on the outer most peaks on both sides the most and usually start at the Jordan side because we'd stay at the Jordan hotel. It's really nice when you stay there because it takes awhile for others to make their way over that far so you get empty trails for quite sometime in the morning. Guess we won't get that perk if we end up having a rental up there! haha
Pay close attention to your pass perks. Use them! Get the pre-season tune! Reasonable discount at ski shop. 4 (on each gold pass) $50 unrestricted day tickets for others. And join “Boyne Rewards” ASAP to start accumulating points, which can be cashed in for a myriad of items. We usually wait until we have enough points for a gift certificate, which we apply to our next season’s passes. Also - major-big perk: unlimited free skiing at BIG SKY if you book lodging there. Many have taken advantage of this. Also discounts at all other Boyne properties in the west.
I will definitely be using any possible perks!! I do have Boyne Rewards, need to check where I am at for points now that you mentioned it! Another perk is free skiing at Brighton in Utah. Since we may attend Diva West next season, I intend on getting there for a day as well to check it out if possible.
Probably not next season. But the following?? Hope hope. This place has been on my bucket list LONG ENOUGH.
