I am wondering what company others have had success with for post cards and for yellow letters.

If you didn't, you should start now.I send post cards 100% of the time.

I am using postcards and to date I have not received any calls.

Definitely cheaper to have us send them. if we ship to you, you'll have to hand apply a .34 stamp on small postcards or a .47 (.49 starting 1/22/17) stamp on letters and large postcards. 

Also well as do postcards or letters work best? 

I finally got serious and mailed out about 250 post cards this week.

Postcards is the cheapest way to go.

Was planning on doing postcards for them if that matters. 

I see same pattern right here in atlanta.I've talked and met with homeowner's who have told me that they're also calling back other buyers from whom they've received postcards., this is driving up prices and narrowing our margins.

My favorite list is people that own the house, live in the house, have owned it for 20 years or more and own it free and clear - that is the house you will make the most money on when grandma or grandpa are now all alone in the house and are moving in with the kids, to the nursing home, or passes away - someone finds your postcards in 6 months or 6 years from now and give you a call to see if you still buy houses - these are the cream of the crop.With Realeflow leads you can do a lot of the above sorting and with the $7 a month version you can get 100 leads from their system - narrow those leads as much as possible before you export them to get the best leads for your money.Then, the next thing to do is to watch the list for returned letters.