I have to go against the flow, and say the 4000 is the best computer. I've owned three A1200s, and one 4000. The 4000 has been more stable, for sure. The 4000 is also worth more on the market, as they can use the Video Toaster.
Sure... It does cost more to fix an A4000 than it does an A1200... But, honestly, at this stage.... Why are you fixing either one??? It's cheaper to buy a replacement than it is to try to fix.
At least for myself, I'm open to offers on any computer in my collection... Except my 4000. period. Granted, a lot of that is sentimental value, but I honestly think it was the best Amiga.