Do I buy Toyota Sienna with the 3.0 l or 3.3 v6?

Actually, on the older Siennas, the oil sludge issue was a head design issue. Many people that were meticulous with their servicing experienced the problem. Still understand that it's a Toyota and it's still a durable vehicle. I've seen so many with extremely high miles that have been neglected and still keep going strong. If you could swing it, I would recommend a 2006 or newer Sienna. Why? They have timing chains, so no dealing with an expensive timing belt replacement periodically. If you buy one that's older, make sure that it has been done or try to get seller to take off $500 or so dollars. You'll want to get that done.

My daughter has a 2002 with the 3.3L engine and except for showing oil consumption consistent with bad break-in it is okay. Look at the other issues for the various generations at http://www.siennachat.com/ . My biggest complaint: the front passenger door refuses to open although I have taken many approaches to it over the years. Overall, it has been the most troublesome Toyota we have had.

Engine sludge has absolutely nothing to do with engine displacement. Engine sludge is a result of either neglect, poor quality oil, or infrequent oil changes. or all of the above.

My only encounter with engine sludge was when using cheap oil in an old car, so now I only use brand name oil like Valvoline, Pennzoil or Castrol -- problem solved. Change the oil+filter every 5,000 miles or 6 months, whichever Sienna you get, and you shouldn't have sludge or wear problems in either Toyota engine.