Alternatives are especially important in other cities. In Tokyo if I want to go from Shibuya to Azabujuban I can take
* Ginza Line->Namboku line - advantages, (1) Ginza line starts at Shibuya so guaranteed a seat if I wait for the next train - though only for 4 stops where I have to switch (2) both lines are same train company so $1 cheaper
* Hanzomon Line->Oedo line - advantages, fastest
* Yamanoto line->Namboku line
* #6 bus - advantages: no changes, disadvantage, slowest
* taxi - advantage: fastest if there's no line for taxis or if I'm confident I can find one quickly
Extra considerations. Each line's station and the bus stop are 3 to 8 minutes walk from each other so if I'm closest to one that would weigh on my choice. Speed matters too, if I'm late. If I have large or heavy packages I'd be more likely to take the cab. Etc....