I've had children on both courses, in fact DD2 has just finished Guildhall kindergarten and is starting their brass training programme in Sept.
RAM: one year of kodaly then two years of group lessons + kodaly. At the end you find an individual teacher yourself (they have some suggestions) and for orchestra/ensemble, can go to ProCorda close by on Sat afternoons. This is what my DS's and DD1 did. DS3 is still at ProCorda's YSE, DS1& 2 went on to CYM near Waterloo, and DD1 went to Guildhall Junior dept. It's a happy, gentle way to start music.
Guildhall: two years of kodaly & dalcroze, then 5 years of either string or brass training (the timetable is 3 1/2 hours of solid music for my DD (age 6) from Sept - I'm waiting to see whether she copes with that). I don't know anyone who wants to who hasn't progressed to the training programmes - it's quite a commitment for the two years of kindergarten and the fall out has been quite large.
Guildhall STP, BTP & kindergarten has more tiger parents but if you can ignore that (or parent like that!) the thorough preparation for music in general as well as a particular instrument is fab. DD2 has thoroughly enjoyed her first two years.
Guildhall Junior dept where DD1 goes, is an absolute joy. She started there age 11 so travelled into London by herself - I think most kids go there without parents so the 'tiger aspect' is diluted by that point. I don't know how many make it into JD from the STP, but I can heartedly recommend it for a child who loves all things music,