How do you mean 'for you', out of interest?
I'm a shift worker and access the internet via 3G in work, and currently use 5GB minimum per month.
So I can keep my current mifi, or use Three's One plan and get unlimited data and free tethering, this means I can put the mifi on a PAYG deal for emergency use.
SIM only option on Three for the One Plan is £25 a month, so TCO including a 32GB phone over 24 months would be £1199.
That vs The One plan on a contract, with Quidco cashback works out the following:
£35/month - 24 month contract
32GB iPhone 4S - £189 upfront cost
£149.98 Quidco cashback
TCO = £879.02 (average £36.63 PCM, £11.67 of that is for the contract, the rest for the phone.)
It's actually cheaper than what I pay right now, which is £20 PCM SIM only with Vodafone and £17 PCM for my 3 Mifi with 15GB of data.
Plus I get to sell the 3GS which will help to recoup the initial outlay.
Personally speaking, I prefer the 'S' model of the phones over the first release, since they seem to fix the "bugs" that come with the first release, and because of that, a 24 month contract doesn't seem
that bad.
Besides, as already mentioned, Apple products hold their value really well, and there's nothing to stop me buying a new phone during the contract term.
Winning all round, for me anyway! Obviously some people don't need unlimited data hence buying the phone outright and getting SIM only is the better option (retention deals even more so).
Everyone is in a different situation and different deals work out in different ways for each individual case, sometimes SIM only and buying the phone is best, other times a contract is best.