Bracers are always there, whereas the Cloak can be rendered useless at times.
I would recommend the following reading material on how to understand the probability behind dis/advantage.
Probability for Gamers (Wall of Text crits you for 500dmg, yeah this guy is thorough).
That article does a great job breaking down the numbers but I will rehash a bit.
Bracers of Defense is a simple calculation an effective increase of 2 on the target die, base 10% difference statistically.
Disadvantage gets a bit muddier and, well it depends on the target number required on the unmodified roll.
Example: If your AC is 18 currently and you are facing a goblin with a +4 to hit you then he would need an unmodified roll of 14 on the die to hit you. This means that statistically disadvantage provides the equivalent of -5 or -4 depending on if you round up or down on the probability.
If you instead had a AC of 22 then that same goblin would require an unmodified roll of 18 to hit you which would be the equivalent, roughly of -3 or -2 depending on rounding.
The above examples are only to demonstrate the changes in approximate penalty to hit based on differing target numbers. They have nothing to do with the Bracers of Defense.
I do have to say that some could argue that the only true -5 modifier is at a target of 11 as the rest should be rounded down. But even then it would appear for the most part that the Cloak of Displacement might be the better choice at this time, but it could depend on what you were facing and the target numbers they were required to hit.
Important note: If you take damage while wearing the Cloak of Displacement its properties do not function until the start of your next turn. So you should factor that possibility in. Note it does not say hit by an attack so that means literally if you are damaged by a spell or trap or anything else you can't avoid you lose its benefits. Also, if you are incapacitated or unable to move. These are definitely things to consider as the bracers are a static +2 AC no caveats other than you cannot wear armor or use a shield.
If you take damage, the property ceases to function until the start of
your next turn. This property is suppressed while you are
incapacitated, restrained, or otherwise unable to move.
Other things to consider
You can only have disadvantage once, no stacking and if your enemy ever has something that grants them advantage then neither applies. What that means if they would only roll one die and your benefit is cancelled. Bracers of Defense can stack with other AC bonuses.
Example: If you have a Cloak of Displacement (that is currently active, i.e. you have not taken damage since your last turn) and let's assume your DM is using the flanking rules from the DMG, two goblins flanking you would normally have advantage which cancels your imposition of disadvantage so they roll standardly.
From Advantage/Disadvantage PHB 173
If circumstances cause a roll to have both advantage and disadvantage,
you are considered to have neither of them, and you roll one d20. This
is true even if multiple circumstances impose disadvantage and only
one grants advantage or vice versa. In such a situation, you have
neither advantage nor disadvantage.
I am sure others can be more eloquent with number magic but I am leaving the linked article as the main course and only narrowing the focus to the question at hand.