Depends on what you want reliable.
Personal accounts give a great insight in the true campaigning, but they also have the huge disadvantage of being...well..personal! I believe account of Walter is famous for being very inaccurate about where they are or where they are going to, pretty much because the low-ranks were barely informed.
If you want to know how terrible the lives of these soldiers were, or for example, what they ate (Blood of a dead horse, anyone?), then personal accounts are Da Shit. Of private soldiers, at least. Captain Mercer of the RHA's account of the Waterloo campaign could also be titled: 'I'm awesome, The Horse Artillery is awesome, everybody else is stupid'.
