I think both locations are great, if they are the same sort of house then i guess you are weighing up the main attributes, being;
double the land vs proximity to the cbd & better transport
so you have to weigh up whether the extra 500sqm is worth more or less than the extra 15km of travel. Is that distance going to make a difference to the future potential of each suburb?
Would also be a good idea to get the opinion of some of the locals in the area, and also do alot of research on the government sites about what is changing in the areas. You will get good growth in the short to medium term if there are any positive changes to infrastructure or amenities in the area.
I like to include the yield when i am weighing up properties, i tend to look for things around the 5% or more mark when looking near the city, further away i look for 5.5 - 6%. If it doesn't achieve this by the nominated purchase price & rent, i look to try and negotiate the price accordingly.
Also i would search both oxley and redbank plains in the search function of these forums, as there's a good chance both areas have been visited extensively in the past
Personally I like the locality of oxley, but there are lots and lots of factors you need to weigh up, including also the condition of the house, the depreciation if applicable, the required maintenance or renovations, the local zoning and also the statistical factors from abs, & government websites about info or changes etc.
GOOD LUCK.