I find the plastic carbonation caps better - they have an inbuilt flange which seals when they are tightened. The SS caps have a normal washer to seal against the lid and, because the edge of the aperture in the lid is quite narrow, the washers can easily become distorted and fail to seal properly. I have three all rounders and find them excellent. If you decide to buy one read the instructions, particularly about suitable cleaners - which do not include Five Star PBW or any other cleaner with sodium metasilicate in. Both Kegland spunding valves are fine, but the one with the large dial is obviously easier to read.