We visited A/B for the first time last Tuesday on public transport (12zl pp each way).
We arrived just before the 10am cut off point and so had the choice of whether to join the 10.30 group tour (40zl pp) or go round on our own with a mini guidebook you can purchase in various languages for 5zl and we made the snap decision to do a self guided tour.
Just my opinion, but I think if Polish or English is your 1st or 2nd language or you at least have a good understanding of either written language you can 'do' Auschwitz 1 by yourself as the guidebook includes a map of the camp and brief description of what is inside the buildings.
Also each significant outside area and each room contains detailed notices in Polish and English explaining what occurred there and/or what you are seeing although many things are, horrifically, self explanatory-I guess it depends how much background detail you personally feel you need and how much information is 'enough'.
Birkenau is different and in hindsight I would have preferred to have a guide, although to see all the camp I think you would need a private guide as I'm not sure the group one covers all areas.
Birkenau covers a vast area and there are not that many explanatory noticeboards and although we all have some idea of the unspeakable wickedness that occured in that place and the evil purposes of the train tracks, unloading ramp and now demolished gas chambers and crematoria there is a lot more to imagine than to see without the help of a guide.
As for getting between Auschwitz 1 and Berkanau there is a shuttle bus that picks up to the left of the car park as you come out of the cafe next to the ticket office.
This runs every half hour or so and is free whether you are on a guided tour or not -there are also plenty of taxis available which cost 15zl each way which is a good option if there are a few of you or you just don't fancy waiting around for the bus.