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If you make your way down to West Ealing, you'll get all the freights coming from Acton and Ealing heading west. I think the next place you'll get a decent selection of freight is probably Tilehurst (other side of Reading) after that.
Ealing Broadway is good for freight near Paddington, but can get a little busy and no access to the fast line platforms any more. Both can be quite inconsistent for workings.
Tilehurst as said above is good further out and gets the Freightliners to the south coast - probably the busiest of the lot and you can get there on a Thames Valley Rover which also allows you to head up and down the line between there and Paddington all day.
Although the view is quite different now with the OLE, but I think the platforms are still open/
I like reading west. You get the freight coming up from the west that doesn't pass through Reading itself (as some turn left and head towards Didcot) and you have the services from Reading that are going to the west and will not pass through Didcot area.