It is feature-complete in every way.
Except for online leaderboards?
The way I approach this question is:
-Is the port accurate?
-Does it offer more than just playing the game on mame?
Thus from my experience I'd say, console-wise
-Darius Cozmic Collection/Revelations (Switch/PC) - M2, thinking of just about every feature you could possibly want in a port. Route maps that highlight the number of power-ups per stage were something I would have never thought about but are life-savers
-ESPRaDe Psi (Switch) see above, the new Plus Mode and new character also make for a nice way to play the game
-Under Defeat/Border Down/Strania/Mamorukun - thanks to the different modes and/or abundance of practice options, these g.rev games offer a lot of value, especially given that no one here will EVER play them on their original arcade cabs. G.Rev probably has some of the all-time best practice modes I have seen in shmup ports.
-Psyvariar Delta (Switch/PC) - God-like practice options, touched up visuals, and an all new arrange. This is one of the greatest shmup ports ever created, and it's a shame that CityConnection has never reached this level of quality again. Only one of the genre's most legendarily good games can deserve such a fine effort. You have no idea how critical it is to granularly set up every practice parameter that matters and practice bosses and stages until you master the game.
-Mars Matrix (Dreamcast) - Another legendary game gets a suitably good port. Shops for scrubs like me, multiple arranges, score attacks, options, control configurations... Not to mention changing the scoring and removing the counterstop to improve competitive play. It feels unusual in how good this port was, given the time period. It feels like shmup ports wouldn't really start being something notable on their own for another 7+ years.
-RayStorm/RayCrisis (PS1) - these two ports do some nice things, in Storm's case, a brand new arrange that's pretty fun, and in Crisis, removing the aggravating map system and replacing it with a more intuitive "choose your route" system. Some may balk at the removal of the arcade's strict TLB requirements for a more breezy "1cc" gate.
-Cotton Rock n' Roll (Switch)
This one is kind of a freebie since the game is new, but the training mode options, which let you adjust rank and a bunch of other options shows that the developers actually like and play these games too.
There's plenty of games I like and ports I like that are nonetheless not what I'd call the "best" ports - e.g. Giga Wing 2 is an awesome game I'll never stop recommending, but lack of true stage practice is a drag. Game Tengoku Cruisin' is another good and fun port but rebalanced from the arcade original which may upset people... and it lacks a proper training mode.