Love XT60's. I've never cared for Deans (or anderson power poles) and have always wondered why those two have such a devoted following as they both seem horribly engineered to me. Deans are a pain to solder, I don't like the exposed terminals (even if it's on the side receiving power), they're incredibly difficult to connect/disconnect even with real honest deans from deans....just not a fan at all. And anderson's while I see some appeal to their design just don't cut it for me, the hard plastic they're made out of is too easy to break and they're overpriced for what they are.
XT60's aren't just compatible with 3.5mm bullets - they ARE 3.5mm bullets. They're just bullets with a convenient molded housing around them that gives them outstanding physical and polarity protection and makes them easy to grip for connecting/disconnecting.
The EC connectors don't look bad but I haven't actually had any to use yet, and since I'm pretty much decided on XT's I'm in no hurry to try EC's. But I would take them over Deans any day.
I started with EC3's since I started with horizon and parkzone planes but once I bought batteries with XT60 I was converted! EC3 connectors are super tight and hard to remove. Deans connectors are small and slippery and the soldering ends aren't convenient at all.
HK sells adapters for XT60's that I bought to retrofit my older planes and charger so I didn't have to resolver new connectors to the existing ESC's in my planes.
As for LHS's they are now starting to carry XT60's since DJI is using them in their Phantoms and have to cater to the people buying those press junkets...