I bought a Motobatt - the first was a dud, but the importer quickly replaced it with another, which works fine. I chose it based on the 'aftermarket shootout' I read online - and yes, the OEM battery is subject to spontaneous mortality.
It is ever so slightly taller than the OEM battery, making thread-starting on the battery clip less than a finger-thread.
The bike starts well and runs, even if I have only ridden a whole hour since installing it.
So, for now I do not regret my decision.
Note that Motobatt warrants their battery for TWO years where Yuasa provides a six month warranty.