Ok Tib,
This is what I would do: Read both.
Personally, I can’t have only one book going at once – I have 3 to 5 good books that I am reading on at any given time. I guess it’s like watching TV (which I actually don’t do much of) – if one program is on all the time, I would get bored to tears. I read the bible at least an hour a day, then I spend about 30 minutes each on what ever contemporary spiritual books I have, and about an hour on one of my favorite novels. (I read A LOT!)
Start both books – give about an hour's time to each and that should get you well into the ‘mood’ of each book. You can then pick up the one of your choice as your reading ‘mood’ dictates.
I think when someone gets used to having several books going at once it really becomes habit. It will improve your reading enjoyment, which will ultimately make you read more.
Of course - this advice is coming from an old guy without a "life".