Having just compared (partly for my own benefit, as I use this route regularly) the various fares that arise by changing from a national rail ticket to a Tfl/Oyster one at each possible stop (Upminster, Barking, West Ham, Limehouse, Fenchurch Street/Tower Hill) the short answer is that it all depends on the time of your journeys. And that it is all completely illogical and that the fares are riddled with inconsistencies.
If you have an Oyster card loaded with pre-pay, AND you are travelling on a Saturday or Sunday, the cheapest way is to get a super-off peak return (valid on any train on c2c on Saturdays or Sundays) from Laindon to Upminster (£4.80) and then touch in on an Oyster pad (and if you are quick enough, get back on the same train), using Pay-as-you-go for the fare to Ealing Broadway (NOT via Paddington main line). This costs £2.40 each way, giving you a total fare of (4.80 + 2.40+2.40) = £9.60 if you do the same on your way back . In fact you could reduce this further to £7.40 (4.80 + 1.30 + 1.30) , if you took a route (ie via London Overground through Shepherds Bush or Olympia) that avoided zone 1.
Either of those fares is a substantial saving on the straightforward return ticket (£11.60)
If you are travelling Mon-Fri, and will be travelling in the peak hour in both directions (meaning: leaving Laindon earlier than the 9.29 train, the first on which off-peak tickets are valid), and starting your return journey at Ealing Broadway between 4pm and 7pm, the cheapest way is to get a return ticket from Laindon to Barking (£9.10), and use Oyster from there to Ealing and back. Presuming that you touch in at Barking between 6.30 and 9.30 am the direct fare to Ealing (again not via Paddington main line) is £3.10 single (£2.40 off-peak). Thus this journey would cost (£9.10 + 3.10 + 3.10) = £15.30 - which is still cheaper than the £16.10 return.
Conversely, if you are travelling offpeak (in both directions) the cheapest place to switch from a paper ticket to Oyster PAYG is Upminster, although in this case the total fare of £11.20 is only 40p cheaper than the off-peak day return from Laindon to Ealing Bdy.
Obviously if you have a railcard it all gets more complicated still.