The oval dome is good if you want two spires, so it's good for if you ever make a dome for sanitoriums or want to have a dome for cloning vats (just have two of the spire and have the entire dome dedicated to cloning as many people as possible) but it also has the three connected large spots arranged slightly different to be one hex "deeper" and narrower so you can make different parks there than you can in the mega domes. Regardless, I tend to have my agriculture, science, and occasionally mining domes be ovals with my industrial ones being mega domes. This is because the network node gives a 20% (plus 2% for every performance over 10) boost to every science building in the dome, the water reclamation system is a huge bonus for a farm dome and food production can be boosted with fungal farms, and mining domes don't require that much space and it gives me room to make everything as good as possible. Industrial domes? You want every single little bit of space possible in one of those for electronics and machine parts factories.
