For the uninformed, which is the best/better codecs?
First, it must be the same codec on both sides, otherwise it default to standard SBC.
Secondly, it depends.
1. AAC.
If you have iPhone, AAC music library and Apple speakers, it will sound nice as everything fit together. On the other side, Android users should avoid AAC, as there is something wrong with implementation, especially with Huawei phones, see link below. Gurus has also discovered that even if the source files (number of bits and sampling speed) are matching AAC codec specification, transfer over Bluetooth is not transparent, so perhaps driver stack is decoding from AAC to PCM, then encoding again into AAC. Complicated?
Besides, downloaded music in AAC format can be hi-res, but Bluetooth codec is just below CD quality (16bit,44.1kHz). If you have an Apple phone, then AAC works fine. you don't have better choice anyway.
https://www.soundguys.com/the-ultimate-guide-to-bluetooth-headphones-aac-20296/
Looking further into Bluetooth transcoding the same format it looks like it is a big mess and it applies to other codecs too, so is you play low bit rates MP3's, don't worry about codecs, all of them sound the same. It is worth to know anyway.
2. LDAC
Android Oreo comes the first time with Sony proprietary high quality codec, LDAC. Huawei phones come with 3 manually selected quality settings, but the quality is adjusted automatically during playing. The highest one claim to encode 24-bit/96KHz audio files, but is approaching Bluetooth limits and the practical range is limited to 3 meters LOS (signal strenght better than -60dBm). If you put the phone in the wrong pocket, connection can break. Normal quality settings is roughly a CD quality, but when connection drops to low quality, it i even worse than a standard SBC codec. Frames start droping at the same -60dBm level, but at a lower rate. In the link below you will see that other codecs have 20dB bigger signal strenght margin. It is a lot...
https://www.soundguys.com/ldac-ultimate-bluetooth-guide-20026/
The article is dealing with number of false claims from Sony. Adding my comment, codec is fine, but do not fit the current Bluetooth implementation well, it can disappoint in practical use.
3. AptX. Qualcomm proprietary. Included in Android Oreo. AptX has a long history, only few years ago was acquired by Qualcomm. It looks like Qualcomm is shifting policy little bit, probably offering it free for MS Windows and (recently) Android. With Windows there is some confusion. AptX codec is included in Windows 8/10, but OEM is responsible to supply drivers compatible with aptX and a license to activate a feature. One poor OEM example is Intel. Drivers for PROSet WiFi/Bluetooth AC7265-3165-7260-3160-826x-9x60 devices are aptX capable, but lack of activation. On the other side the same Intel wireless devices supplied by Dell do work. It can change soon, once Sony came with LDAC - competition is good....
AptX is definitely better than SBC. It fits perfectly in the current Bluetooth limits. Much less intermodulation distortions, it really differs from all other codecs. Wide freqquency response will preserve harmonics in the original source. Encoding takes little CPU resources, unlike AAC/LDAC. See:
https://www.soundguys.com/the-ultimate-guide-to-bluetooth-aptx-and-aptx-hd-19914/
AptX HD version is little bit better, but not really hi-res audio as Qualcomm claims (neither LDAC is). Variation AptX LL is low latency - 40ms. The new version AptX Adaptive will scale a quality depending of the connection quality and content playing.
There is no many AptX HD headsets on the market. I decided to get a good shells with aptX from Sennh%^&.
