I've struggled with this dilemma for a long time. I finally pulled the trigger and bought iPad 4 16Gb Wifi-only. I haven't yet opened the box as I'm waiting for the accessories to arrive.
I've read through dozens of threads about this question. Unfortunately, it is my feeling that many answers are misleading. Not all of us want to store the sama data in every device. Not all of us have huge music and video collection. Not all of us keep apps that they don't really even use (I mean who uses 5-10 pages of apps regularly). The problem here is that when people who are so-called datahoards are answering to questions posted by those who do not necessarily store that much data in the iPad, the latter group thinks that even a 32Gb-model is too modest.
Let's think about this from my own pespective. A 16Gb iPad will have 13-14Gb of actual space. If you aren't into hardcore Retina apps and don't have time or will to use dozens of apps regulary, you will struggle using more than 2Gb for them. The first apps I'm going to download will be Quickoffice Pro HD (under 50Mb) and two Monkey Island -games (357Mt/game). That's about 800 Mb. If you add a dozen more apps, have only 1-3 games at a time, it's hard to get beyond 2Gb. Next, photos. Well, I would probably test the iPad's photo abilities and use the Retina-display to view other phots, but I doubt I would ever have over 50 JPEG photos in there. Music? Nope, I use my phone for that. So we are still at about 2-2.5Gb used. I know people are saying that some apps will bloat in size in the future, but that is not going to mean that 2Gb will turn to 4Gb. We're most likely talking about games and speciality apps (such as iMovie). Finally, videos, and we have 13-14Gb - 2-2.5Gb = 10.5-12Gb of space left in the iPad. Videos do take a lot of space. I recently Handbraked a 1.5-hour movie with "Apple TV 2" preset with stereo-audio only and lowered the bitrate/quality to 1400 which was still okey for SD/DVD according to a couple threads. The file size was 1.25Gb. In other words, I could still fit about six SD movies in there. Of course one is tempted to use the iPad's HD Camera to shoot 1080p video, but from what I've understood, you need to shoot a long clip before megabytes turn into gigabytes. I'm not into filming that much as I'd probably just shoot 2-3 clips of 0.5-2 minutes a year.
I think I've made a pretty good case for the iPad 16Gb. You do need to manage files (delete games you don't play and movies you've just watched). On the other hand, it just seems a bit much to pay Apple $100 for the 32Gb when I know that I would never be beyond 20Gb usage even if I tried. Moreover, I bought the iPad as a secondary device that I'd use when writing my university papers on the go and surfing/playing/watching movies modestly when I travel. I can also use iCloud and DropBox although in my country Wifi isn't everywhere.
Still, I must admit the 32Gb tempts me a bit. I just know that I wouldn't be happy if I constantly saw "20Gb of free space" in the settings.
