I am an oil guy and the only boiler I would use is Grant - the Vortex model. You can get it in a 21-26 kw to suit your job and it could be adjusted at commissioning to whatever power in that range you require, using appropriate nozzle size and pump pressure etc to MIs.
I personally prefer to use a standard Grant boiler and put any sealed system components (exp vessel & filling loop etc) outside the boiler if possible, which makes servicing easier later, but not essential.
Reason I opt for Grant boilers is they are well built and fairly easy to service as they are simple but clever designed. (The flue gas route from main heat exchanger to secondary exchanger is cleverly designed using a single door).
They have high efficiency and proven reliability.
Unfortunately though they are not made in U.K. but actually are all made in Southern Ireland as far as I am aware.
Worcester Bosch HE oil boilers are over complicated and too expensive.
I dislike Warmflow boilers because of their design and other problems.