Mirror glass is commonly used. It's flat and cheap. There isn't really a sudden thermal shock to worry about, and if you're going to be printing at temperatures that need borosilicate glass, you might find the aluminium parts of the bed sagging. Remember to ask for the edges to be smoothed.
Thinner glass will transmit the heat better - but you might be able ...
People choose borosilicate because of its thermal properties.
Between ceramic and tempered, I would suggest tempered glass, it's not good as borosilicate when comes to adapting to rapid temperatures but better than ceramic. The other option I would suggest will be "Aluminium", which is much better.