As you can see, you will get every man and his dog on here, all with different opinions of which to go for. There is no right or wrong answer.
Vaillant are in my opinion the Best you'll get but they are the most expensive. Some would say the same about Worcester. ( a bit like Audi v BMW I suppose)
There are mid range boilers of course which have been around years like Glow Worm, Ideal, Baxi etc, ( Vauxhall, Ford, mid range type thing, No offence, my vans a ford) normally one or two hundred quid cheaper.
Then there is the lower end ( naming no names ).
I think you get what you pay for, a lot of course, comes down to budget.
However ...........The individual who installs whatever your budget will allow, is a massive part of it. That bit is not like buying a car at all. My advice to you is to find a Highly recommended Heating Engineer to come round, see the job and advise you on what they think is best for you.
I hope this helps a bit.