VMotion is for a situation where everything works, and continues working. It allows to move a VM to another ESX, for load balancing or host evacuation. There's no dropped connections, and no reboot. However, as soon as an ESX isn't there anymore (HW crash, ...), forget about VMotion, it can't help you anymore.
HA is for a situation where an ESX goes down. The VMs that were running there go down with it, instantly. Other ESXes in the same cluster will react by restarting the crashed VMs. This involves a reboot of the OS, maybe a file system check, and the starting of the application. Obviously all connections that existed to the VM originally are dropped.
FT is for a situation where an ESX goes down. A protected VM runs on one ESX, but has an identical twin (secondary "shadow" VM) on another ESX. If the primary VM goes down because of an ESX crash (HW crash, ...), the secondary will instantly become primary and continue the workload. There's no reboot, no dropped connections. There are a lot of limitations to FT, including max 1 CPU in the VM, etc.
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