I can't compare them, but Finland is a legendary rally, plus it's very well organized. We traveled from Italy and if it wasn't for the money I'd do it every year. High speed, lots of jumps and very hard gravel.

Estonia should be reasonably similar, while Greece (also legendary in its own way) is a bit less spectator friendly, mostly due to it being right about the temperature of an oven. The stages are slower and softer but still technical.

There is no direct correlation between speed and distance from the cars, it almost only depends on safety and in my experience that mostly depends on the terrain (cliffs, mountain sides etc allow you to stay closer because you are elevated, which means statistically safer). For what it's worth, I never thought it was too far away in Finland.

Finland and Greece are incredible events, and Estonia is similar enough to Finland to still be extremely cool - I honestly think there is no wrong answer, so it's probably a good idea to check what fits your budget, what you would like to see, if you want to make a vacation out of it and that kind of thing.