I can only speak to US vehicles mostly. I know GM started using 3g cellular connections (that no longer work) somewhere around 2008 and later. For repair-ability and parts availability somewhere under 2010 I think is a good spot. You also get some of the newer safety features if that's on your list. But most cars in this era are heavily computerized, except for your more budget model stuff. 

Fully computerized engine management (throttle is fully electronic) electronic traction control with differentials and braking systems that are expensive when they break. 

90s into 00s is the newest without computers being too intrusive, but more likely to fail due to age, and parts are harder to find, especially computers. I have hoarded at least 1 spare electronic module for my truck for this reason, they are so hard to get PCM's for, and I usually have to program them because the correct ones are too hard to find.