The Schengen lounge is the nicest lounge as far as 'looks' and facilities are concerned. However, at EU flight peek times (7~9am and 6~8pm more or less) it can be quite crowded. This goes for all lounges as the non-Schengen lounges can also be crowded at times (last week was standing room only!).

A nice advantage of either of the two non-Schengen lounges is that you have a very good view of the tarmac.