Gen tech was the most difficult for me because a lot of the information was new to me. Reading the book twice and doing a lot of practise with the confuser meant I managed to scrape a pass first time. I'm reading it all again to make sure it stays relatively fresh in my mind. I didn't find Air Law difficult, but it was very boring - I found the most effective way of getting to sleep was to read that stuff.
I thought Nav was the most fun and it was also the exam in which I did best.