montipora digitata and montipora capricornis tend to be forgiving, there are some acroporas that are easier than others.....I would suggest a green one in color off the top of my head....they seem to hold their color well compared to the more vibrant ones, there are some tan ones that can be quite interesting that have highlights, so don't overlook those. John, (he runs the store for his wife), is very knowledgable and has alot of frags that are perfect for what you are looking for. He will be more that happy and able to suggest some great pieces for you to start out with.
I would try not to spend a lot on on particular piece right now and do more of a quantity thing so you can "get your feet wet". Try to avoid any wild pieces and ultimatly you are looking for a tank raised piece or something he has had in his system for a while. They tend to be the most forgiving and stable in color.
Watch out, its an addictive hobby.....especially with the SPS. Best of Luck, and don't hesitate to ask any questions here if you run into any problems......there are a bunch of people here that are very informed aquarists.