I recommend P20, it is a fantastic product and I have never been burnt when I have used it (except under the arm where I missed a spot) and I have been using it since 1997! It lasts all day no matter how many times you are in and out of the water (sea and pool) or if you are doing watersports. The only downside is that when you get out of the water and lay on your towel, it tends to turn light coloured items yellow.
However, as already posted above this year I am going to try the Piz Buin - All day long, apparently that does not turn your clothes yellow and I will be able to let you know at the end of May as I go in 10 days time!!! Yippee!!!
Another product to try is the Malibu range, which is very good, especially the after sun with insect repellant - I have never been bitten using this product, it smells nice, it goes on smoothly and it dries quickly. If you want it to be even more affective, leave it in the fridge, it is unbearably cold, but it does the job.