Sian Berry - had the authority on the subject that you'd expect from a Green Party leader, and could easily have set and lead the agenda; she did admit, however, that while the Green Party have long-established expertise in debating and strategising about carbon emissions and climate change, they haven't been as hot on biodiversity crises.
Plaid Cymru guy - enthusiastic and convincing about the party's recognition of issues involved, and their passion to do something about it if in power.
Nicola Sturgeon - as she herself reminded Krishnan and the panel, she's the only actual leader of government currently, and she pretty convincingly listed various active and developing SNP green policies, while recognising areas of the debate they need to address more concretely.
Jeremy Corbyn - came across as tired and a bit grouchy but managed to affirm various aspects of relevant Labour policy and of course bigged up their plans for a Green Industrial Revolution and how nationalisation to some extent connects up with green issues. Was taken to task over Labour's more distant emissions target date of 2045 (ie. the Greens have the closest target date, and some of the others are more ambitious in that respect than Corbyn's manifesto.) Slightly cringey moment when Corbyn waved a hard copy of the relevant Labour green policy and Krishnan and Sian Berry chuckled that it would've been more environmentally friendly just to read it online.
Jo Swinson - can't really remember, but she waved her arms about a fair bit and said "y'know" a lot, as per.