Database: They should as fast as your database
Gettext: Backward-compatible with the po (however - we do not guarantee
100% compatibleness). It has a lot of tools for editing. Since 0.0.4 it
can be used as a development provider and in production it may be
exported into database[1]. However be aware that 0.0.4.x are relatively
broken and many bugfixes will be in 0.0.5.
Yaml: Nice syntax?
Regards
[1] Possibly in some version there will be possible to choose provider
on base of enviroment