IMHO - you will get solid advice at a good forum for a specific make - sorry. So many people on those forums have had cars and can't just compete with places like Edmunds. I would go with Kelly/Edmunds to get general ideas then go to specific forums. You will have to find the good people among the chaff of jackasses that abound at every forum.
For BMW - the folks at E46Fanatics have several forums for other newer series (like the E90x series and now F series). BMW also has a magazine (well the BMWCCA does) called Roundel. It is fantastic and does not tow the BMW company line because it is not a BMW owned/run magazine. Near the back is a column by Mike Miller:
»www.bmwblog.com/2010/10/18/inter ··· agazine/
Fantastic guy and advice... See if you can get a hold of magazines - heck - you can probably email Mike Miller directly and he will answer any and all questions you might have about a BMW - new or old with no sugar to make the news go down easier.
I own an older E46 330i (2001) - I do love it and I bought it with just under 150K miles. They have things to be mindful of - cooling system will need to be replaced every 100K miles. The headliner will likely fall if kept for a long time. The early years of the paddle shifting automatics - sucked (I have a true manual). I know the earlier M 3's (E30, 36, 46) need their valves adjusted about every 30K miles. Not sure about the newer E90 and F series.
They will have sensors - tons of them. Newest BMW's don't have an oil dipstick or a spare tire - but then many of the newest cars don't have them either. This is one reason my 3 series will probably be my only and last BMW. I know my oil level sensor is bad - I know it is bad because I can use the dipstick to check. Can't do that with the newer BMWs.--
"It drops into your stomach like a Abrams's tank.... driven by Rosanne Barr..." A. Bourdain