I wasn't aware you could buy straight from the publisher but it's definitely something I'll look into. As regards what suits me best, the cheapest price of the book I want will be what suits me best.
I'll definitely check out them sites you mentioned as well.
What I did notice though is that e-books aren't as cheap as I thought they were going to be. On some sights I came across e-books that were actually more expensive than the paper copy, which doesn't make sense at all! But thanks again for the info..