I have an iPad, and a portfolio web site, and I like to keep my portfolio in both places. For one thing, viewing my work on the iPad is a lot faster than relying on an internet connection in many places.
I don't know if it' "the best," but I have "Portfolio" for iPad
, and it works pretty well. I can control the look of the splash page, have multiple galleries, and it's reasonably easy for a first time user to navigate. Note that creating galleries is MUCH EASIER if you use the Dropbox functionality with Portfolio. (That is, create a folder of photos on your computer. Name them whatever you want -- it's easier if they are numbered in the order you want to display them. Upload the folder to your Dropbox folder. On the iPad, in Portfolio, use the Load from Dropbox setting and choose the folder. This works a LOT better than going through iTunes and using photos in the native iPad photo app. I discovered this the hard way, of course.)
To answer the "why an iPad" question, it was given to me at work. (I know, that doesn't answer the question.) After the first couple weeks, I was having some second thoughts, but now after a couple of months I've found it very useful. Of course it's great for email and calendar use -- much easier than a tiny phone for responding to emails, for example. It fits in my camera bag, so I always have it with me. I can read or surf the web while waiting or at lunch, or I can check the weather for a shoot tomorrow, or check the sun and moon angles using The Photographer's Ephemeris app. We used the GPS and Google Maps app while traveling over the holidays, and I have used that app to check aerial views of potential photo subjects. I use Evernote and Dropbox to organize and update all my files and folders and anything I need to remember. I use Skype to talk to my daughter in France. I could, if I were so inclined, download about a million games, so if that's your thing, the iPad can apparently do a nice job with gaming.
I'm still trying to get Shutter Snitch and the Eye-Fi cards to work on the iPad. Our wi-fi at work doesn't have any open access, which for now makes it impossible, but there are several possible solutions that I need to try. That will let me send photos to the iPad during a shoot, so an art director or the subject can view them. That would be very useful for me.