Reserved train seats London - Newbury?

It has been a few years since we traveled extensively by train in the U.K., but then I bought the Advance tickets well ahead, and then went to the station days ahead of travel and reserved the seats ( no charge).

On those occasions since, when we have traveled without seat reservations, we have never been unable to find a seat.

GWR doesn't give you a seat map or the ability to select. If you indicate you want to reserve a seat you give a number of parameters (window or aisle, forward or backwards etc) and you are allocated with them before paying if reserved seats are still available (some carriages are non-reservable). No seat reservation is the default unless you are buying Advance type tickets.

Not all of the trains to Newbury offer reservation; the ones on commuter-style trains don't.

Unless there has been a problem on the line and trains have been cancelled (in which case, seat reservations will probably be cancelled) or if you are travelling during the rush hour, you will get a seat and will not have to stand, therefore you don’t need seat reservations. Just be sure that you are at the station in plenty of time.

You will have the advantage of boarding where the train starts its journey from at Paddington station,
Newbury is commuter distance, for myself i would be comfortable to turn up and go with an off-peak ticket, which is a mainly flexible ticket.

The tip I'd give is to arrive at Paddington in good time and check the departure board to see if a platform number has been allocated, otherwise monitor the board and as soon as your train platform is shown make your way swiftly to the train (others will be doing this too)

On board you pick your own favourite seat position , might be forward/rear facing/table/aisle/window/sunny or shady side,

As mentioned, not all train stock is the same, the local stopping trains aren't the same as the faster inter city trains.

Thank you all for the feedback. I purchased the off-peak tickets. It looks as if there is no reserve seating on this particular train. However, the tickets say space has been reserved for us.

Finally heard back from a CSR at GWR. The trains from Paddington to Newbury and back is are considered "short journey" and therefore no seats are reserved. It's first come, first served, so we will take the advice of getting to the stations early for best seating. Thanks again for your advice.

That would be the case for the services that go no further than Bedwyn, but not say the 18:03 that goes all the way to Penzance. I guess you are on one of the former type.