Should I use current prices or volumes estimates?
If you are conducting empirical exercises, you should use real values i.e. volumes. If the data has time dimension, it is even more imperative to deflate the variables. The reason for this suggestion is following:

Take output data, over time output changes and usually around a rising trend. The trend growth of output could be due to rising prices instead of volume of output. The following image shows the effect of inflation on output:  



The nominal GDP grows at a relatively higher rate than real GDP. The economy appears to have grown, in fact, much of this growth is due to rising price levels, not due to positive growth in volume of output. Using the data from the graph, you can see that 


nominal GDP in 2012 is 1.3 (=16000/12500) times that in 2005, that's
a 28% increase in GDP.
real GDP grew by 8% only. 
in the same period, prices rose by 18.5% (=1.28/1.08-1).


This shows that the volume of GDP, real output, did not grow as fast. The nominal GDP, on the other hand, gives us false impression that the economy is growing at a faster pace.

If you are using the data in statistical or econometric exercises, you should use volume data in constant prices. 

And, if you are comparing performance across countries, you should convert the data to international dollars using purchasing power parity (PPP). I think OECD database offers PPP based macro-variables