Hmmmm that is a very difficult question,lots of variables to consider
The way i looked at it a 3.5g ( BR prototype) is a good size engine to carry, but is low down in the pulling stakes for passengers. However a 3.5g narrow gauge is up there with the 5in (BR) ones but not as heavy
Also 5in gives you a bit more to work with ( consider N and OO gauge)in effect making the small bits are larger ,if that makes sense. Years ago 3.5 was the default size but with the advancement of home eqpt ( Lathes/mills) 5in seems to be the preferred size Again Size of lathe might dictate size of driving wheels and casting costwise there isnt a vast amount of difference in price. some engines are 'harder' to do than others. I would guess that on here there is an example of every design built or in progress
Any questions just ask, but at the end of the day it will be your choice,you may have a childhood favourite ( personally i would love to do an Ivor the Engine!!) look in the Blackgates site they have a good selection there to start narrowing down your eventual project
Thanks reply Ron and for your advice which is most welcome.
Childhood favourite was definitely the Bulleid light pacific West Country class. Our farm was either side of the Barnstaple to Ilfracombe line so was a daily sight often with a banker in summer for the climb up to Morthoe. Happy days.
I think the Bulleids are lovely engines. Keith Wilson did a series (a rebuild) in the ME some years ago, and there are some 'errors' which have be listed by several builders and i believe are readily available. However it isnt the first one i would pick. Looking at the middle cylinder machining gave me nightmares, BUT they are out there and good models too. (perhaps it might be an idea to lok for part built ones on ebay
Like this example of another pacific being built on this forum
If i wasnt up to my knees with my B17 i would have that like a shot it is daylight robbery!!
Met Bert Hooker several times and he had tea with us when he came to give talks. A real Gentleman. The upside is you have full size ones to take plenty of pics of. Which gives you plenty of excuses to get out to the preserved lines!!