There are probably two ways to encrypt your computer full disk encryption which completely locks down the computer between when it is off and when it has booted but after everything loads you computer is not encrypted anymore and then there is something like a file encryption which it only encrypt files in a virtual hard drive or a folder or something like that and even if the computer is booted the file or folder is still encryption so which is more secure a full disk or a file encryption?
You can't compare Full Disk Encryption to File Encryption as they are both different things.
One encrypts the entire drive, the other only affects targeted files.
If you want to be more secure, you could use both.
This Wikipedia article should assist in choosing encryption software that suits your needs:
Using full disk encryption is very much recommended, but it all depends on what you are protecting and the impact level, full disk encryption would protect you as long as your device is not on active state(after you entered the key),for example it wouldn't protect you if someone on the same network had accessed your files since you have already entered the key, but you could use here as an additional precaution file encryption, and encrypt also the files which are important for you to not be accessed by anyone, and decrypt them only while you are using them.
So use both if neccesary.