Which Worcester Greenstar boiler to choose ?

[Ionized]

I presently have a Greenstar 24i junior installed, it's probably about 12 years old and getting cranky, the engineer suggested upgrading it to a 30 model sometime, but he just realised that the gas pipes would need changing (from 15mm to 22mm).

My question is, which model would you suggest replacing it with that would be the least hassle ?
Thanks in advance.

 

[ShaunCorbs]

24 ri as they still make it or the baxi 825