All services stop at all stations to Paddington in the COS,
The main changes happens outside the COS, more so on the west.
Heathrow T5s will Skip Acton Main Line, Hanwell and Southall where as Heathrow T4s will stop at all stations on the way to Heathrow.
Reading services will Skip Acton Main Line, West Ealing, Hanwell usually.
Maidenhead services will Skip Acton Main Line, West Ealing, Hanwell and Taplow.
There can be slight variations with the Reading services, the 17:46 and 18:12 which are both classed as the fast Reading services:
Will Skip Acton Main Line, West Ealing, Hanwell, Southall, Hayes & Harlington, Iver, Langley and Taplow.
From what I know of these are the consistent stopping patterns from origin stations(Shenfield or Abbey Wood):
Reading Fast
Reading Semi-Fast
Maidenhead Semi-Fast
Heathrow T5 Semi Fast
Heathrow T4 Slow
Paddington Slow