I have quite a few tattoos. I have monarch butterflies in various stages of development (from caterpillar to cocoon to butterfly) on a milkweed which takes up my outer bicep, top of my shoulder, back of my shoulder, and in my armpit. I have a large gerbera daisy with song lyrics around it in the middle of my upper back. I have a dolphin, seahorse, and waves on the inside of my left arm and into my armpit. I have a pawprint with an eye inside on my lower right back. I have a hunny pot (yes... hunny... from Winnie the Pooh) on my right butt cheek. And finally, I have Calvin from Calvin and Hobbes on my right calf. I am much too lazy to post pictures of them all though.
The most painful spot for me was an inch over from my spine on either side. To date, that is the only tattoo that I have had to break up into two sittings due to the pain rather than the size.
My advice to you is to make sure you go to an artist that you know and trust. If you have friends that get tattooed, ask if you can visit/watch for awhile and get a feel for the artist's personality and the way s/he works. Find out how long they have been tattooing. I know everyone has to start somewhere, and just because someone has only been tattooing for a short while doesn't mean they're a bad artist... but wouldn't it be nicer to go to someone who's been doing it for years rather than months? Let others be the guinea pigs.
Make sure the tools are properly sterilized, and that the needles are new. A reputable shop will have certificates posted showing that their sterilization equipment is tested regularly. The artist must wear gloves while working, and will change their gloves if they touch things that are not sterile. My artist wraps everything in plastic while he works, including his telephone. He also keeps all needles in their package and only opens them once he is ready to start tattooing. The artist you choose should do the same.
Look through the artist's portfolio while you are there, paying special attention to see if there are pictures of healed tattoos rather than fresh, still red tattoos. This will help you accomplish two things. 1) You will be able to see the true quality of the tattoo and get an appreciation of how the colours actually look, as they are distorted by the redness/swelling of the skin when they're fresh. 2) You will know that people who go to the artist are happy enough with the artist's work that they went back to see them again.
Finally, don't choose where you put the tattoo based on the pain factor. The pain is temporary, and the tattoo is forever.