I haven’t tried Boost, but I swapped over to Summit and have been pleased with the experience. The thing I liked most about Sync was the amount of customization; Summit fills that space quite well.

Boost is nice but I can’t deal with the lack of swipe gesture actions at this point in time. No other app has been a perfect substitute for Sync but after trying basically all of them I find Summit to be both the best right now but more importantly - the most promising for the future. Very active dev who is responsive and accommodating user requests.