Arecibo has been superseded in terms of raw aperture by FAST, and in terms of angular resolution by the interferometry arrays since 1966 at the latest when the One Mile observatory was doing 23 arcsecond resolution images. I think it's main somewhat unique capability was doing radar measurements of things in our solar system.
My impressions is the neglect comes from having done all the useful things it could do ages ago, and not finding anything new to help with in the areas of science that gets funding.
The state of the art interferometry arrays are ASKAP and MeerKAT currently, in the sense of being the newest and being precusors of the SKA which is the biggest project right now.
In terms of best in class, it varies with the specific frequency and which bit of the sky you want to look at and also with what you consider an observatory: the Event Horizon Telescope that resolved the M87 black hole has the worlds best resolution at their mm wavelengths, but it's really a bunch of existing telescopes collaborating and not a purpose built facility.
My impressions is the neglect comes from having done all the useful things it could do ages ago, and not finding anything new to help with in the areas of science that gets funding.
The state of the art interferometry arrays are ASKAP and MeerKAT currently, in the sense of being the newest and being precusors of the SKA which is the biggest project right now.
In terms of best in class, it varies with the specific frequency and which bit of the sky you want to look at and also with what you consider an observatory: the Event Horizon Telescope that resolved the M87 black hole has the worlds best resolution at their mm wavelengths, but it's really a bunch of existing telescopes collaborating and not a purpose built facility.