which is faster?

Space trains are obviously the fastest.

Is this a quiz? If so: what can I win?

rapid and express trains are only something like trade mark or trade names. it depends on where that train is. in Poland for example rapid trains are fast trains calling only in 'bigger' or 'more important' stations, express trains are more comfortable trains, calling in cities. but the speed depend not on the name of the train but on the tracks which it's going on. the real fast trains are TGV in France or ICE in Germany but only if there are separate fast tracks for them.

so 'rapid' or 'expres' means not much more than 'not local'. but this is different in France with their RER-trains where the 'E' stands for 'express' but it's a suburban train anyway. as u can see it's just the definition, that doesn't really say much. :D:D

which is faster?
It's the same thing.
During the '80, SNCF created 2 kinds of trains: "Rapids" were faster (and more expensive) than "Express" but it's over.

Exactly, those names are synonymous, or are interchangeable. To me express feels more like a train that skips stations, and are shorter distance, and rapids are longer distance and actually go fast. That's just how it feels to me though

They are not the same

At least not in Japan.

Heirarchy goes vaguely something like this:
Local(普通／各停）
Section Semi-Express（区間準急）
Rapid（快速）
Semi-Express（準急）
Commuter Semi-Express（通勤準急）
Express（急行）
Commuter Limited Express（通勤特急）
Rapid Express（快速急行）
Limited Rapid（特快）
Semi-Limited Express（準特急）
Limited Express（特急）

There are so many different companies and so many different service levels and obviously one company does not use all of these on one line (Odakyuu and Seibu use a lot of them though, Odakyuu operates Local, Section Semi, Semi, Commuter [Tama] Express, Express, Rapid Express, Limited Express Romance Car (special fare), and Seibu runs Local, Rapid, Semi, Express, Commuter Express, Rapid Express, Limited Express New Red Arrow (special fare), so while there is a pattern it is not easy to keep track). Rapid is slower than Express.

What's the question?

Are you saying Rapid trains are the skip-stop trains and the express are skip a LOT trains?

Chicago has dozens of express trains between the suburbs and the city. The city has one main express line that skips around 10 or 12 stops on it's elevated system. There use to be multiple skip-stop lines back before 1993. The stations were either A or B or AB stations. The trains were either A or B trains. It was good for shuttling the trains faster overall as they only had to stop and open the doors every two stations.

They gave that up though and made everything all-stop in the 90's.

I thought an "express" train was one that didn't stop until it reached its destination, whereas a "rapid" train was one that went fast.

After all, you have "mass rapid transport" (MRT) in Singapore, for instance, but the overall speed would hardly break world records.