Lake Placid or Whistler

I've never raced Placid so I can't help you there.  I haven't raced Whistler yet but we just spent a few days up there a couple weeks ago.  Incredibly beautiful venue.  But if you don't like long, sustained climbs and/or fast, sometimes technical descents then stay away from Whistler.  I have heard also that lodging options in Whistler are more abundant and cheaper.   We found a nice condo for pretty cheap.  I'll be racing Whistler in 2016.

If cost is a concern go with Whistler. IMLP hotels fill up and the raise the prices with usually 4 night minimum. Hotels that are basically old 1950's hotels charge over $200/night and are places normally we'd never stay at. Other option is a big venue that IM week doesn't make a dent in housing available so prices are reasonable and closer to the start there are more rooms or condos.

Renting a house or condo is an option but again very expensive and price is much higher IM week than other weeks.

I did LP and my family enjoyed it. But after doing other IMs my kids like others better. Town gets closed down for IM and it is challenging to get around IM day.

Are you flying or driving? Again LP is a bit challenging to get to if you fly.

Town, scenery, locals, and course are all nice in LP. I personally prefer more rolling hills instead of the long climbs in Placid.

I've done Whistler twice.  I've never done Lake Placid but I grew up near there and have been there a few times.  I know dozens of people that have done it and always listen to feedback because I'm always interested in doing different races.  There have also been numerous threads on ST asking similar things.

Both are very beautiful areas.  Whistler is stunning.  The whole area looks like it should be on a postcard.  Lake Placid is a couple notches below Whistler in that regard.

Travel: Whistler is much easier to get to assuming you're flying into both venues.  Fly to Vancouver and drive the 90 minutes.  It's a spectacular drive.  There aren't any big city airport options near Lake Placid.  Burlington, VT, Albany, NY, and Syracuse, NY are the nearest airports.  Burlington's airport is very small.  Albany's is bigger, Syracuse's is a bit bigger than Albany's.  Both Burlington and Albany are about a 2.5 hour drive.  Syracuse is about 3.5 hours.

Lodging: This isn't remotely close.  Whistler is a world class resort town.  It has a zillion hotel or condo options and the prices are not what I call cheap but it's not bad.  In 2013 I stayed at the Hilton.  Had a 700sqft room with a full kitchen and it was $250/night.  in 2014 I stayed at the Pan Pacific Whistler Village Centre and had a 900sqft 2 bedroom, 2 bath, full kitchen suite and it was about $320/night.  Sort of pricey but you're getting modern 4-star resort level accommodations without price gouging.  At Lake Placid you pay $300/night for a 1960's Motel 6 that I wouldn't stay at for free, let alone $300.

Swim: I heard the swim at LP is really nice.  Whistler's swim is more than decent but I think people give the edge to LP.

Bike: East coast mountains are not the same as west coast mountains.  The Adirondacks are not the Canadian Rockies.  Placid is hilly, and very hilly in parts.  Whistler is mountainous.  That stated, the elevation gain at both is similar but it's how the gain comes is important.  

Run: I can't really say anything about the run at LP since I haven't done it.  Whistler's run is nice, very picturesque, and pretty hilly.  It was a challenging run.  

Dev Paul over at ST summed up LP vs MT vs Whistler very well: 

Here is my background with the three venues: 

IMLP 11x racing, 30x or more training 
Tremblant 8x racing, 7x training 
Whistler 2x racing, 3x holiday/training 

Lake Placid 

• Best course of the three in my view that balances difficulty/easiness/lack of drafting
• Pavement quality is good again aside from a few sections
• Worst price gouging for hotels
• Hardest to get to if you fly, easy to get to if you drive from North East cities
• IM takes over the town but there are distractions other than IM like hiking, bobled run, Whiteface mountain, fishing, hiking
• Most hotels in walking distance to race venue
• Perhaps the BEST finish line in triathlon. Better than Kona coming into the oval
• LP sells out early....it is within 50M people who can drive
• LP is the most crowded course
• After the race in LP you can extend vacation in the Adirondacks, Lake Champlain area or Vermont within a short drive

Tremblant 

• Best race organization of the three
• Smoothest pavement, hard riding at the end of each loop
• You can't beat Quebec culture when it comes to events....they just know how to do events. Quebec just knows how to run a party. This is probably the best IM "party" in North America.
• Most drafting of the three. On the highway 117 on loop 1, the Tour de France/IM Florida affect is in full view. Loop 2 is much better on drafting, but still annoying.
• Best family venue for kids under 10
• IM takes over the town, but there is some other stuff to do hiking and mountain biking on the mountain
• Hotels are fair priced, accomodations are easy access to race venue. Many places with no minimum stay
• Tremblant has no grocery store on the mountain. It does not have Starbucks, it does not have Subway, it does not have McDonalds....I know some of you won't care, but for others, easy food options
• Tremblant does not even have a Tim Hortons on the mountain....WTF this is Canada (OK, it's Quebec, but get real....)
• Tremblant does sell out, but a bit later than LP. It is in driving distance from around 25M so does eventually sell out so don't wait forever
• Tremblant is moderately crowded relative to LP
• You can vacation in Montreal or Ottawa after the race. Both great places to visit. I grew up in Montreal....can't beat partying there.

Whistler 

• hardest race course with close to zero drafting. Pavement quality is good. Scenery is beyond stunning on a sunny day.
• Race organization is good, but with a two transition set up, more painful for families with young kids
• Resort is like Tremblant but on Steroids+EPO+HGH. Whistler is a world class mountain resort in the same group as Vail, Chamonix, St. Anton etc....everything else is wannabee. You gotta take the Peak to Peak Gondola between Whistler and Blackcomb
• There are a zillion things to do in Whistler outside of IM. I find I like that, and my family certainly does....hikes, rides up the mountain, tubing on the river
• Lots of real restaurants and a real grocery store on the mountain. Every chain fast food place is there
• You have the Sea to Sky Highway in and out of Vancouver....that alone is beyond awesome and many people fly from Japan, China and Europe, just to see some of that
• Weather like all three resorts can range from crazy heat wave to insane cold. Whistler will never get too humid like LP and Tremblant. But Whistler can get insanely cold like we had this year. That was 3 days of freak weather in an otherwise all sunny summer
• Whistler does not sell out generally. It is just too far from 50M who can drive over quickly. You could register until Sunday 7 days before this year's race
• Whistler is least crowded on course
• Vancouver itself is a reason to come over to Canada. There is a ton of stuff to do there post race.

Don't forget if you pick Whistler, the exchange rate for U.S. folks is pretty favorable (1 USD = 1.33 CAD as of this post).  Helps with the registration cost, too.