Which tag format to use?

I recently bought a new album and went to update the tags using MP3Tag. I noticed that this time saving the changes did not add APE tags. I've always used ID3v2.3 (ID3v1, ID3v2.3, APEv2), but this latest album defaulted to ID3v2.3 (ID3v1, ID3v2.3). I'm not too concerned because it hasn't affected my music player at all, but it set me to thinking what are the best tags to use? Can/should I remove APE tags from all my music? What is the general standard for players these days?

Unfortunately, there is no "general standard for players these days".
It depends only on YOUR players. The one in your car, in your appartement, your mobile phone and so on.

I would say: For most .mp3 files, you don't need APE** tags. But again, it really depends on your devices.

** The APEv1 tag was designed for the Monkey's Audio format.
** APEv2 allows metadata values to be Unicode rather than simply ASCII in APEv1

That's not completely true.

If you're using mp3 you should know.
ID3v1/ID3v2 was first tagging format for mp3 and designed to work with mp3 (uses synsafe int values to avoid interpretation as audiodata).
APE was introduced by Monke's much more later and is NOT SUPPORTED for most Audioplayers (Software and Handware).

ID3v2 supports unicode, dynamic tag lenght, covers and so on
ID3v2.3 is a de facto standard that is even supported by Windows itself and most hardware devices.
ID3v1 is the older format that support just fix lengh Ansi Tags but is support by almost any devices, even hardware devices.

Do not use APE for mp3 files, you will get compatiblily problems and may corrupt files.

Interesting. As far as I can tell it doesn't cause any problems at the moment, but I'll bear it in mind if I start to get any. Thanks.

And there is also the issue of some players not being able to displaying data from every tag field, even the legit ones

An example from my own experience:

Bear in mind that tools like mp3gain, foobar2000 and liquidsoap do store ReplayGain values in APEv2 tags in MP3 files.

I’d still recommend getting rid of APEv2 and ID3v1 tags in MP3s, and use other tools like loudgain for replaygaining or foobar2000 with APEv2 tag writing disabled.