The most efficient way to regulate unregulated 12V
The battery voltage will vary as a function of state of charge. So, if your load cannot accommodate for that range you need an interface dc/dc converter, and being the load 12Vdc the converter must have buck and boost function. Consider that while charging the battery the voltage should approach that 14.5V you mention.
The Tracopower isolated converters are not so efficient, if I remember well. Your TSR1 is non-isolated and advertised with 0.94 at Vin,min (9V) that is a pretty good figure, instead.
Isolated converters have lower efficiency: as a comparison Murata NCM6 gives 84-86%, and this above 40% load level (measured with respect to 6W). Recom REC6 are very close to that. It is more or less a good standard efficiency level to use as reference.
The non-isolated versions in principle are more efficient, but much depends on the amount of information the manufacturer provides. For example the Cincon EC5A does not go better than 87%, and I think in the best operating conditions, but no clue which ones. Your Traco does not show curves as a function of Vi and load % either.
Generally speaking in case of a custom design efficiency for a dc/dc converter of this kind may be improved by: reducing voltage drops across diodes (Schottky, correctly selected for low VD at the operating current), even using synchronous rectification at the secondary (the used MOS would reduce by far the voltage drop), low DC resistance of inductors and transformers. For a quick hands-on solution, instead, use commercial products.