Bluetooth or not


Just purchased new cell phone just wonder about connecting , 3.5mm head phone jack to preamp input or Bluetooth which is the way to connect to get the best sound?
bluetosman
i've always felt that the wired connection is  better than bluetooth, tho the difference is much less with the newest bluetooth aptx codecs (provided your devices support them)
Wired is better. However, do not rely on the inbuilt DAC of most phones (Iphones are OK but most others not). As long as you are not hoping for the very best, but only for a big improvement with most phones, get a Behringer UCA 202 external usb DAC in between the phone and the amplifier for much much better sound (if you can get a usb signal out of your phone).
See here for more detail on Bluetooth quality: http://archimago.blogspot.nl/2017/12/measurements-oppo-sonica-dac-and.html
It will depend case by case. DAC used is the biggest factor. Newer Bluetooth technology can be quite good.   Traditionally, wired has greater upside.   Try both and see.

Using a good outboard dac with wired connection is probably the surest bet for best sound. I’ve gone that way with a Chord Mojo DAC. Not only is it great with headphones but as an input to a good hifi as well. I went for bust and connect it to line level inputs using a very high quality Mogami gold mini stereo to dual RCA Y adapter. The results are absolute top notch.