I started ordering manga from Amazon before using TBD. They were always fast but the books nearly always arrived with a slight knock because the books moved around in the boxes. Nothing too bad, though - I could always tell the books were unused.
I then discovered TBD, who are nearly always cheaper. I started out by receiving a damaged Naruto set, getting a £18 refund. I then received a mint Death Note set. I followed that up by ordering NHK 2-8 from them, and they all arrived mint. My luck then started to do a 180 with Confidential Confessions, with nearly every volume having knocks or rips, one even having yellowed pages and looking used (I got a free replacement copy, but that was just as bad.)
In my experience, TBD have a lot of stock with damage and yellowed pages. They mix them in with the stock they should be selling for new prices. I don't know how they store older books but they sure don't look after them.
At first I was fine with the up and down service because of their speed, but for months now they've taken 5 days+ on average to send anything I've ordered. That, together with my local postal people seemingly being determined to damage anything sent in jiffy bags, means I'm often left waiting a long time for a damaged book to be given to me, and I then have to make a dramatic complaint in an attempt to get as much money back as possible.
While Amazon books will more than likely arrive with a few minor knocks because they aren't secure in the boxes, I can at least rest assured the boxes wll provide far better protection from the RM than a few small bubbles. And Amazon have always been fast to send, like HMV, so I don't have to worry about sending speed.
...of course, the books may very well still arrive damaged because of damage done on the journey from America to the UK, but there's nothing I can do about that. I just have to hope I get lucky.
As for Play, them sending my Planetes set to me in thin cardboard packaging and it arriving with a nasty dent has put me off ordering from them. HMV are usually very fast with pre-orders, usually have slightly better pre-order prices, offer excellent service and make sure art boxes don't get damaged. Why order from Play instead when you have to do a Google search just to find a CS email?