This is a question that we all come across as teachers and, I think it is not a matter of better or not but they are different according to your goals and targets in your musical education.
If you want to pursue a career in music or you want to build a solid music foundation is better to go with the ABRSM as it seems to be more complete since the early stages. The sight reading is compulsory from Grade 1 whilst in Trinity it becomes compulsory from Grade 6. I will try going in order through the different parts of the test.
Scales and Arpeggios
ABRSM syllabus there are more keys to play in similar motion plus contrary motion and various chromatic scales. From Grade 6-8, thirds and sixth part are introduced alongside contrary motion scales in all keys and chromatic scales in contrary motion too. As for the Arpeggios, more keys are required plus first and second inversions in Grade 7 and 8.
In Trinity exams, the numbers of scales and Arpeggios to performed are more limited but they require to perform them in different dynamics and articulation which encourage the musicality development. Also the number of contrary motion and chromatic scales are more limited than ABRSM. In the technical requirement there are three short exercises to be performed which focus on voicing, fingers strength, coordination, balance, wrist flexibility.
As for the technical part of the test, it seems that ABRSM focuses on the technique, knowledge of the key signatures, fingers dexterity whilst Trinity seems to develop some aspects of technique alongside developing musicality.
it is quite evident that the ABRSM choice of repertoire is very classical and based on the tradition of classical composers except for the C list where it focuses on more jazzy, bluesy, dissonant, contemporary pieces.
Trinity syllabus offers a wide range of pieces in the style of the Baroque, Classical or Romantic pieces composed by contemporary composers. However, there is also a few range of pieces by classical composers. It seems that the Trinity offers more appealing pieces for the modern taste. In both syllabuses, the requirement for the test is to perform three pieces in a varied range of mood and style.
in ABRSM sight reading and Aural test are compulsory whilst in Trinity there is a wide range of choice amongst Aural Test, Musical knowledge, own composition and improvisation up to Grade 5. From Grade 6, sight reading becomes compulsory. Again, it seems that Trinity focuses more on the musical development and creativity rather than the technique and theory knowledge.
These come with Pros and Cons; I must admit that training a Trinity student for a Grade 5 sight reading from scratch is not easy task as I think it is a very good habit to start from the beginning as it is a skill that needs time to be developed and improved. At the same time, I enjoy teaching the Musical knowledge where the candidates are asked questions about dynamics, musical signs, key signature and modulations in the pieces they have performed. I think this is a very good way to improve a sense of analysing the music one is performing.
As for the Aural Test, the ABRSM needs a lot more work for non singers candidate as it is very important to develop the inner ear and be able to think about the sounds in your head and being able to reproduce them. In Trinity, there is not any singing involved and that can be easier for students who are shy in front of an examiner outside their comfort zone.
I hope you will find these information helpful and a guide on your syllabus choice.
Written by Sabrina Curpanen, piano teacher at WKMT