all the above options will do, but some added thoughts for you
- you mention photos, only laptop will work for serious photo editing, but all will do photo viewing (iPad will need camera connection kit)
- you say batter life is important... really? if you have a motorhome, can you not charge from that whilst on the road? I'm guessing you will just need a 9v charger, and all/most options will work from that.
- coverage, if you are traveling off the beaten track, all providers will have high/low points (assuming you use one of the top 3), but usually you can get somewhere to get a signal if you move

- contract... a lot cheaper, per day - and will give you discount on some items (e.g. iPad or smartphone), but then you are locked in... you could possibly get multiple PAYG sim cards, and use whatever you need. (assuming your device is not locked to a provider)
- price... what you are willing to spend will determine your options
- reuse after the trip, given all options work, which is more useful to you later.
- if you get a iPad, make sure you get a micro sim from the provider (they have a nasty habit of giving a standard size sim!)
personally, id say
smartphone - if you really are going to use very occasionally (e.g. check email, and the odd bit of internet), though you will be surprised how flexible they are (e.g. good camera, good apps)
iPad/tablets - if you want portable and low hassle, again pretty flexible
laptop - if you want more to do more powerful things (e.g. photo editing) or more reuse when you get home
others will disagree, but i personally found netbooks to much a compromise - more hassle than a tablet, and not as useful as a laptop... (you can get some pretty light/thin 'proper' laptops these days)
whatever you get, make sure you have it a few weeks before you go away, so you are very familiar with it before you get on the road
as they say, you pay your money and takes your choice
