What envelope should I use for my next Yellow Letter Campaign?

[Ivan Lopez]

In the past I've used these envelopes for sending out my Yellow Letters but they are quite more expensive. 

I'm looking at switching it up for my next campaign to one of the ones below they are about 50% cheaper. I would love to get your opinion on which one you think i should use. Im personally learning towards the brown recycled paper looking one. 

[Justin Silverio]

In my experience, there are 3 critical components to a marketing piece.  1) Get your prospect to notice/open your mail, 2) Get them to read your message, 3) Get them to take action.

Your question relates to #1.  The invitation style envelopes with a handwritten mailing address will stand out from other mail because of it's shape and indication that it's a personal mailing.  Keep in mind that some colors will stand out better than others.  If you really want your mail pieces to stand out, you can create a design on the front and use a specialty stamp.  It may cost a bit more up front but you'll get a lot more engagement due to the mailer's uniqueness.