[Android Software/Hacking General [Developers Only]] scandiun:
Here I will post the advantages and disadvantages of the two.

Advantages of UMC

UMC works at block level. It means that you access the partition from the operating system like if were local, and you have complete control of it.

For the previous reason,

UMC keeps timestamps for files and folders

. This is specially important for pictures, photos or videos that don't have EXIF, where you rely on file creation or modification time to arrange them and to know when were taken. MTP sets for all transferred files current system time, thus overwritting the real creation or modification time and ruining your gallery.

UMC allows the

use of recovery software

(Recuva) or partition software (Easeus Partition Master) and even format with a different filesystem. Without UMC you have to use android side software that usually is less powerful, needs a rooted phone, etc.

As you have total access to the partition, you can

access all files

there, even hidden, system, etc. With MTP you only have access to the files that the controlling operating system (android) wants. For example, with MTP, files starting with dot (.file) are not accessible. Some file formats are not allowed.

UMC is compatible with any operating system that allows connecting a FAT32 / exFAT pendrive, while MTP requires specific support. Linux and OS X may have built-in support or not.

With UMC you directly access the files, so

modification is instant, and viewing

. On the other side, with MTP you download it, modify it and re-upload the edited version, but you never do it directly. Even to play files you need to completely download it first. Imagine downloading a 5 GB MKV.

UMC is always the same, while for MTP there are several implementations: MTP, MTPZ (Microsoft Zune), Sony SonicStage, Apple DMAP.

UMC is faster

than MTP because requires less time to initialize transfer, but isn't that big difference for an average user. The higher the number of files to be transferred and the lower the size of each file, the higher the ratio MTP/UMC.

Advantages of MTP or PTP

In MTP mode, the android device controls the input/output to the filesystem, so there is

no risk of data loss

because of cold disconnecting the device from USB. You work on a layer over the filesystem. With UMC you must be careful.

MTP allows you to

use the sdcard from both the android phone and the computer

at the same time, even to any desired number of them. On the other side, with UMC you only can do it from a device at a time, meaning that you have to unmount the sdcard from the android to view it on the computer, stopping apps, etc. Of course there are software that can force viewing UMC from both sides, but is a highway to corruption.

MTP

does not show the native filesystem to the computer

(it uses a hierarchery simulated by the MTP driver), so it will always be compatible. For example, on devices with the same partition for data and sdcard (like Galaxy Nexus, Galaxy S3) you are writing from the computer to an ext4 partition and you don't need windows to support it. The same if the device partition were in any imaginable filesystem, the MTP will show you it in a standard hierarchy. On the other side, with UMC your local operating system (windows, linux, mac) must support natively the filesystem of the partition or download some software that allows you to do it.

With MTP you use all capabilities and disadvantages of the device filesystem. If the filesystem is in ext4 you can copy files over 4GB to the device, that you couldn't in UMC mode because usually it will come formatted in FAT32, that is the most compatible fs for all operating systems.

MTP enables Windows Media DRM, UMC doesn't.

MTP allows the use of password for accessing the files (on compatible devices). On the other side, with UMC, of course you could use powerful tools like TrueCrypt, but you need the corresponding software on android that reads it.

How to preserve timestamps

- Use File Timestamp app. Root is required, and works recursively too.

- Use Mass Storage Mode when possible.

- zip or tar the files when sending them to the phone or receiving from.

- If the device has external sd, you can use it as a man in the middle.

- samba (smb protocol) allows preservation of timestamps, however applications for android don't support it.

- FTP allows preservation of timestamps, however applications for android don't support it.

- NFS allows preservation of timestamps, however couldn't get any application for android working properly (Servers Ultimate Pro).

- Rsync allows preservation of timestamps, however couldn't get any application for android working properly (Servers Ultimate Pro).

- adb push and pull does not preserve timestamps. Furthermore doesn't work recursively with folders.

- MTP does not preserve timestamps.

- Cloud services like Google Drive, Dropbox, etc. usually never preserve timestamps.

Questions and answers

Is possible to implement MTP on "put here your device"?​

Possibly yes, if has USB. MTP works on software side, so updating your rom or installing a new one will do the job

Is possible to implement UMC on "put here your device"?​

That depends on hardware mainly. If the internal sdcard and the data folders belong to the same partition, you can't. The reason is that you can't enable access to a part of a partition at block level, the whole or nothing. This is the case for Galaxy Nexus and Galaxy S3, in order to take advantage of all space, and discard the case where you have filled a partition and the other plenty of space.

Sources:

Easy UMS, USB Mass Storage and Media Transfer Protocol – XDA Developer TV

DifferenceBetween: Difference Between MTP and MSC

Directions on Microsoft: What is MTP?

CrackBerry: On startup - Media Transfer Protocol

Ice Cream Sandwich supports USB mass storage after all, Galaxy Nexus does not

Issues and questions:

[Q] Hidden folders through Android MTP

Nexus 4 not showing files via MTP

[Q][MTP] Certain files/directories hidden to windows file manager?

Connecting to PC files are different!

MTP and hidden files

[Q] Hidden files and MTP/Windows

[Q] Do the S3 still using 2gb partition for data and 12 as virtual sd?

Just got meself a Nexus 7... But!

Upload to dropbox: file timestamps should be preserved

Android File Transfer - For Mac users only