If you are talking a 300 Turbo, the 3.07 is the most plentiful of the two ratios that are most compatible with that engine. However if you were thinking N/A 300, then the best bet would be the 3.46 that should go with that engine. There was some talk about ratios recently, and most finally agreed that 240's and NA 300's don't readily support ratios other than the factory applied ones. The 300-DT's have two available, but there is not a lot of difference between them. The existing 240 ratio would not be a real good candidate for either 300 engine.

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150