This is my opinion only!
I fit 90% Worcester Bosch because of the following reasons:
1) Very good to fit
2) Pleasing on the eye
3) Extremely reliable! ( I have suffered less than 1% failure rate during warranty period and I fit two a week on average)
4) excellent controls
5) Excellent after service care
6) quality performance does what it says on the can
7) excellent range for all occasions, - wall mounted, floor mounted etc
I also rate vaillant and veissman but not as much as WB
See he likes them, yet ive been 2 8 in last year with pin holed blocks, so this is a problem with the way are built, worcester are now made from budget plastic parts yet stll charge top whack, not exactly what they say on the tin
Fitting easy, so are all boilers, replacing parts on them, awful so people will charge you more to fix
just my opinion