For actual numbers, confirming that Sony is not a price leader, see
How does Amazon, B&N and Sony stack up on ebook prices post agency model. However, Sony, Kobo and Borders all sell Adobe DRMed ePubs, so in combination they may be competitive.
Striping DRM from B&N ePubs is easy and I don't think B&N can change their DRM to make it harder to circumvent (since it is now in several 3rd party devices). They often have the cheapest price, and have some ebooks that other sites don't (Sony also has some exclusives).
Stripping DRM from Kindle ebooks is relatively easy with K4PC and skindle, but Amazon does seem the most proactive DRM supporter and it has updated its DRM several times already. If you want the largest range of legal ebooks, then the Kindle store has to be on your list but it isn't the easiest for ePub consumers to deal with.