I used to use 'Easy Diabetes' on my phone, and logged everything. Took over my life!
Now I have a pump I use my pump handset to do all my working out, and it stores the data, so I'm not tempted by a separate app any more.
I did like the Easy Diabetes app, but it did rather fuel my obsession for meticulous logging.... which I suspect would have applied whichever app I had gone for!