Hi Lloydelee,
I find the Penguin Guide to be a bit conservative though it is consistent. Do you remember the Schwann Catalogue for classical recordings? I really liked that catalogue and I was nearly devastated when it stopped publication because I would look through each quarterly issue backwards and forwards before placing an order with the local record store. The advantage that the Pinguin had over the Schwann would be that the Pinguin reviews and rates its CD's. The advantage that the Schwann had over the Pinguin is that it listed everything that was in print, therefore making the Pinguin catalogue seemingly minuscule by comparison.
The point that I'm driving at with this comparison between the Schwann and Pinguin is that if the Pinguin were to comprehensively list and review all of the excellent recorded performances available, then it would end up being the size of six unabridged dictionaries. Consequentially my collection is less mainstream in nature from that of the Pinguin entries and recently I've been relying on the reviews in Gramophone, Fanfare, etc... before making a purchase.
The Pinguin however is consistently dependable if there is a work that you aren't familiar with. Lastly, the Pinguin seems to choose most of its CD's from the corporate labels and less from the boutique labels but admittedly I have not seen its recent edition.