From my experience, I would avoid a coach/organised tour if at all possible. You end up being rushed around in a group, with often not enough time to see everything, and more importantly, to take it in.
My experience of Auschwitz was of being quickly moved from one horror to another, with no time to reflect or take a breather, and the end result was either emotional overload, or somehow switch off. I found I couldn't do the latter, and it made it very difficult for me to complete the tour. It really is horrific. Especially when you go straight from block 11, the punishment block to the small gas chamber at Auschwitz 1 (the only gas chamber not to be destroyed by the camp guards before deserting the camp). There also wasn't enough time, so we didn't get to see the remains of the gas chambers at Birkenau, and the selction platform we only saw from the distance of the guard tower.
If you can, take a train to Auschwitz and then take a bus, or walk the mile to the camp from the station. Pay for an individual guide when you get there, it's not too expensive. I wishe we'd have done it that way. If you want to stay anywhere fairly close, Krakow is the nearest large city, and is a beautiful place. Unlike Warsaw, it was left virtually undamaged at the end of the occupation.
Hth!
