There are a variety of things that could impact your decision, but it mainly boils down to two things, the first being;
On a let only basis, the agent will be responsible for marketing the property and finding a suitable tenant, arranging the tenancy agreement, dealing with referencing processes, registering the deposit and collecting the first months rent in advance.
This is a good bit of leg work out of the way, however, on a let only basis the agents responsibilities pretty much end there.
They will probably deduct their fee from the first months rent that they have collected, forward the money onto the landlord and then their job is complete.
From then on the landlord is responsible for everything - from collecting rent to dealing with maintenance.
If you are happy to manage your own property beyond the marketing aspects, and you have the time and the know-how to do so, then let only might be for you.
If you would rather sit back and let a reputable agency take care of the tricky bits, then perhaps fully managed is the way to go.
The second question that you need ask yourself is;
This one is pretty self explanatory; is it actually possible for you to manage your property due to geographical separation?
If your property is in another town, city or even country, then it may be unfeasible to manage it yourself, and full management might be your only option.
Despite this being the more expensive option, it can sometimes be the best choice - even if you aren’t separated from the property.
Full management comes with various benefits, including guaranteed rent in some cases - it also reduces a lot of headache!
You can simply give them a percentage and allow the passive income to roll in.