Hiya! It's up to you! I am using the pink book called "The Beck Diet Solution" - it's not a diet but it teaches you to think in such a way that it helps you to stick with whatever diet you choose for yourself.
I'm not sure that swapping between different diets is necessarily bad. I think you would have to allow your body at least a few days to get used to what you are eating whenever you change though. How long are you staying on the diet before you swap? And are you switching straight on to the next diet or having a break in between (which may possibly be undoing some of your hard work?)
Is the first book the pink book? Called The Beck Diet Solution? That's the one I've used successfully before, and I'm hoping it will arrive in the post today (if not I'm sure it will be here tomorrow). I gave the original away to a good friend.
How about reading it through with me? I'm going to read through the first 14 days of lessons this week and while away on holiday, then start reading a lesson each day from day 15 on the 28th March, when I'll also be restarting my diet (NoS).
Have you ever tried NoS? Its a simple plan. No Sweets, Seconds or Snacks except Sometimes on Saturdays, Sundays and Special days. That's it! The website is www.nosdiet.com if you want to check it out. No need to buy anything, it's all on the website. No special foods or equipment or books or anything! Just training yourself to eat "normally" :-)