After more then 3 months with the SGS2, I have to say I am starting to miss my iP4.
Yes there is much more to tweak, but most neat features of Android make an already poor battery life completely unbearable.
With the latest jailbreak tweaks for iP4 (IntelliScreenX and Zephyr) you get notification and multitasking functionality that's unheard of in Android.
I am still using the S2 as my primary phone (with a bigger battery on the way) and holding out my final decision until Samsung releases official ICS build, but so far I think that for my daily use I would get more out of the iPhone4.