Ok, longtime Android user, I recently switched to the iPhone 5
I can't comment on plans, as UK plans are very different to the ones in France.
(I pay 17 quid/month for unlimited calls, unlimited texts, and 3GB of data, no contract)
The price does not include the subsided phone, so you have to buy it full price.
I chose the iPhone 5 over the 4/4S for several reasons, one is the lightning connector.
After 10 years of using the dock connector as standard, Apple has moved to a different and better connector, over time accessories for the old connector will fade away.
I've heard complaints about battery life, but I'm damn impressed by mine.
I get at least a full day out of it, most of the time 2 days, but when I'm working. (and bored) I spend a lot of time on the phone. (unlimited plans have that tendency)
Currently: 3 hours of use, and 22 hours on standby and 64% battery left.
it's an overal solid phone, runs nicely. The 4/4S will be a bit cheaper, but by how much, and how long will you be using it? I wait about 6 months after release to buy any new gen tech, since often there are some teething problems. (antenna gate anyone?)
So waiting for the 5S/6 is not really an option, since it's apparently delayed, so say a release in 6 months, with my 6 months that's one year for me.
You said you wanted an iPhone, so I'm not going to suggest any other phone
But get the 5, it's pretty future proof for a few years.
Apple still does updates of iOS for the 3GS, which came out 4 years ago.
Just my 2p,
M.