Reaming is quicker and can be done in a trimmer with the proper cutter. Turning requires a separate tool and takes a bit more finesse.
In my experience, if the brass is not even in thickness, the reamer will 'follow' the off-center hole and what you'll have in the end is thinner neck walls that are still non-uniform. If the brass is uniform, reaming works well. (Reaming will also remove 'doughnuts' if your brass develops them -- but lets not start solving those problems unless we know that we have them.)
The turning tool OTOH cuts to a mandrel and you can be fairly sure that you'll get uniformity -- but it's more work and you have to understand what you're doing at least a little bit.
All you're doing is creating brass that will accept the bullet and retain the needed clearance. I have found that most factory chambers are loose enough in the neck that necking down a caliber or so will usually not require thinning the neck walls (by either method). In fact, you may well wind up with a better 'fit' by leaving the brass full thickness -- but you HAVE to know the dimensions and the clearance that you have in order to be safe.
Make a chamber cast and measure it. Then measure your loaded rounds.
Frankly, unless you're talking about a high quality custom bbl with a carefully cut chamber done by a knowledgeable 'smith, running for minimum neck clearance is usually like putting lipstick on a pig. There are far more important loading considerations for a factory silhouette rifle.
