If you'd like to use the tablet "anywhere" then yes, you need to ensure it's 3g.
The iPad is a mighty fine device for most purposes. I would suggest just going for it with 3G because:
1. Easy to use.
2. Tons of people have them, so advice is widely available
3. Android tablets can be hit and miss.
If you're going to look at an adroid tablet stick to One of the Samsung tabs or the Google Nexus (as suggested by Trig - please check it's 3g before buying though, if you think you need it).
You've also got two sizes to consider, the big tablet which is around 10" or the smaller type which is around the 7" mark. Which do you need?
Eastern, you can buy some handy little plugs for SD/USB for the iPad (attaching a usb keyboard makes it an actually useful piece of kit for work!). For photographers the ability to pop the SD card out of your camera and into the iPad to immediately see your photos is really useful. I'm not saying this functionality isn't available on androids, but my experience is that everything on android is a right faff!
has, you may also, if you're happy without 3G, want to have a look at this:
http://www.microsoft.com/surface/en-gb
If you're one to use a lot of MS tools then it could be a winner.