Fantasista and Initial D, have very little in common on the outside, for starters, ones about soccer and the other deals with drag racing. However, underneath this exterior, they have very specific things in common. Both have main characters with extreme amounts of raw talent for their specific sport. They are both too young to be that good, and have honed their talents by practicing their whole life on their own. The stories began this way, and develop with both characters going from great, to amazing to astonishing in their feats. Also, they both gather friends/rivals who equal them in skills, producing high tension, and action pact races/games.
If any of these things are what draws you to one, than I greatly recommend you check out the other.
First of all both titles are about drifting. I believe this is enough to convince fans of this sport to read them. In both series there is a lot of attention to technical details and some parts might be hard to understand for some, while others will find absolutely nothing interesting in knowing about a character's car's horsepower. However, if you like cars and like drifting (and you really don't have to be that much of an expert to understand both mangas) you'll find both Initial D and Over Rev really interesting.
Both stories are entertaining and will have you wanting more. The main difference is that Initial D is generally more serious. There's a lot of fuss about what a street racer should and shouldn't do. Also, each volume ends with a cliche cliffhanger (although the story as a whole is by no means cliche) like before a race. That can get a little bit frustrating.
You have to remember that Over Rev is a few years younger than Initial D and the older title even gets mentioned in it. Both series are about people who are extremely talented in drifting, but another main difference is that Over Rev concentrates (quite surprisingly, for a manga about cars) on female drivers.
To sum up both titles have a lot in common are are worth a read. Still, both appeal to a certain audience and others will probably find them uninteresting. Give them a try, though! As Over Rev proves, drifting is also for girls. If you haven't read either, I suggest starting from Over Rev as it is lighter and less detail-packed.