How to choose an iron distance race?

Here are a couple things to consider:

-Do you want to do an Ironman branded event?

There are 140.6 distance races in addition to  the Ironman brand. These are usually smaller venues but very well run. Some say do an IM branded event for your first one, this is all up to you. IM events are more expensive to enter (around $700), non branded events are cheaper ($200-$400).

-What kind of course, conditions, or location would you prefer?

The IM Arizona course is very different from St. George. Conditions vary between the two. St. George is know for it's climbing, Arizona is pretty flat. Some venues are known for warmer humid conditions, others are cooler and dry.

-How much do you want to spend getting there?

Your info says that you are in MA. Traveling to eastern races may be cheaper compared to coming out west. Also, factor in if you will be traveling with family and the cost to house everyone. Some venues have cheaper housing options. Lake Placid and CDA have more limited housing options so the costs may be higher than Tempe AZ and FL. If money isn't an issue you might consider an international race.

-What are your racing strengths?

Are you a weaker swimmer? Some courses are wetsuit legal, others are not. Some are current aided. Are you a strong climber? Maybe Ironman Canada or Lake Placid will suit you. Ask these questions.

-Do you want to make a vacation of the trip?

There are venues all over the world, if you plan to extend the trip and vacation consider picking a venue you actually would want to spent more time exploring.

Most branded events require signing up a year in advance, if you're considering a 2013 race date be prepared to make up you mind fairly soon as the US circut starts this spring. When it comes to signing up you may want to actually go the year before and volunteer (factor in additional costs) or plan to have your credit card ready to go when spots become available (as many races sell out in minutes).

Sounds to me like you may want to consider IM Florida for an Ironman brand event or look into Beach 2 Battleship for a non-Ironman brand race.

Full Disclosure:  I have not raced either of these events, but I have done an IM brand race and was very pleased with my experience.

Heat is always a possibility in the afternoon, but humidity doesn't have to be.  West will get you drier conditions.  That'd be CdA, St. George, Canada, Arizona and Bend if it gets added.

I haven't done Lake Placid but from what I remember of NY, there's quite a bit of humidity in the summer.  It's a toss up on how warm it will be, though.

Actually, this would be one of my primary factors.  The training is FAR more important than the nature of the course or the (expected) weather, in most cases.  Taking that into account, it makes any IM much earlier than LP a challenge.  Of course, this also likley puts you in a window where weather is likely to be on the hotter side.  Perhaps something late Sept, like Chesapeakeman is worth considering.  LP is beautiful.  It's going to be one of the easier ones for you to get to (which is nice).  It will be expensive as LP boosts rates during IM week and most hotels impose minimum stays.

Out of these 3 races, I would definatly choose rev 3.  I did it last year and loved it.  Cool water highs in the low 70's.  No humidity flat course, great rest areas and community support 1/2 Im going on at the same time gives the race an even biger feel.  Great floridian is a good race but few participants and you will feel alone at times.  I admire them for sticking through IM florida  moving in their backyard though.  These were the two I Narrowed it down to because I do not like heat and I don't regret my choice.

Good Luck