For the battery connectors, count me as an XT90 convert as well. I'm switching over batches of batteries and a vehicle at a time, but I like them for everything except perhaps small stock buggy where lightweight everything matters. I think if I ever get back into stock racing I'll either stick with inboard 4mm bullets or use XT60s. I've used deans, but also agree they're more of a pain to solder than it should be, even though I don't generally have issues with them.
The XT60s are nice, but are a 3.5mm bullet connection, which I don't feel comfortable pulling the amp load of 2s 4wd SC or eBuggy Lite through. The EC3 and EC5 connectors are named after the size of their bullets. The XT90 has the largest mating surface with 5.5mm bullet connections. The XT90 is SUPER EASY to solder, even when using 8 and 10 gauge wire instead of just 12. They stay together well, but have good grip points so still aren't hard to pull apart, and are reasonably inexpensive as well.