There’s actually quite a big difference, certainly from a debugging point of view, between the connection not working at all and the connection working but then dropping - which I think is what you’re saying about your Bluetooth connection.
I don’t use Bluetooth with Blynk, as (1) it doesn’t fit-in to my use-case and (2) as far as I’m concerned the functionality isn’t reliable enough.
I for one would like to see Bluetooth dropped from the Blynk product, but it is possible that your disconnection issues are caused by bad coding.
As far as WiFi connectivity is concerned, this is extremely reliable when implemented correctly - assuming you have a good WiFi and internet setup.
Maybe if you shared the code that you’ve tried for both Bluetooth and WiFi connectivity, along with information about what you’re seeing in your serial monitor, then we’ll be able to help further.
Pete.