Full Idea
It makes little difference, at least in extensional contexts, whether the truth bearers are propositions or sentences (or assertions). Even if the bearers are propositions rather than sentences, propositions are structured rather like sentences.
Gist of Idea
Propositions have sentence-like structures, so it matters little which bears the truth
Source
Leon Horsten (The Tarskian Turn [2011], 02.4)
Book Reference
Horsten,Leon: 'The Tarskian Turn' [MIT 2011], p.23
A Reaction
The 'extensional' context means you are only talking about the things that are referred to, and not about the way this is expressed. I prefer propositions, but this is an interesting point.