Which Mercedes to start with?

[93Ford]

So the plan is to eventually have a 350-400hp om606 but which car would be best suited to that, the w210 vs the w124. Theres plenty of rust free w210s that show up around me, in the long run are they worth building over the w124. I like a smoother and quieter ride but some decent handling would be good to have. Are some w124s better/easier to swap the 606 into than others, should i look for the 93-96 model that has the na 606 and swap in the turbo model or is the 2.5 and older 603 better to use as a starting car. It would be a DD and driven a lot 60-100 miles a day and i live in the ky mountains so lots of steep hills and twist and turns. Curious to see your opinions.