Time Capsule

The two most recent gen TCs are faster than the two earliest, due to triple-stream 5GHz wifi radios (450Mbit/s theoretical - usually small fraction of that in reality.) The most recent TC gives the best performance of them all. To get this level of performance you would need a Mac with a tri-channel wifi transciever built into it, that means 2011 model year and onwards AFAIK. Otherwise you "only" get 300Mbit/s.

Even with full 450Mbit/s link speed, you probably wouldn't want to do huge file transfers wirelessly regularly, it's still much, much slower than wired gigabit ethernet.

As for wether your first TC was set up incorrectly, who can say. Impossible to know without access to a flying Delorean. Probably it was set up correctly because there simply isn't that many knobs to twiddle to screw things up in Mac products, but rather using standard b/g wifi technology - which is VERY very slow by today's standards.

Also note that all wifi performance is dependent on many factors, like where your computer is in relation to the base station; clear line-of-sight, any walls and composition of said walls inbetween the two, metal objects in the vicinity, other nearby wifi networks from neighbors or businesses, and in the case of standard 2.4GHz wifi, the amount of cordless phones, microwave ovens, games consoles and handhelds, smartphones, garage opener remotes and a host of other gear creating interference.