If you are wanting to initially log on your iPhone or iPad after a flight and then later up load to PC I would recommend MCC Pilot Log. I have been using it for both professional and private flying for over a year now and find it very good.
Buying the enterprise version gives you access to an online sever to save your logbook to, aswell as having it available on your phone or iPad. Cost me around 500 norwrgian (ca. 40GBP) with no further subscription fee´s.
It was great for me as I had a PC at home and all other logbooks for iPhone only worked along side a Mac. Since then I have switched to Mac and use a program called Parallels to run windows in the background, allowing me to continue with MCC.
Have a google and you can download a trial version for free.
HH