Activity tracker best for Cycling

Okay, in that case, the best recommendation happens to be the easiest one: Go with Strava, and don't do anything else. It is *not* perfect, but it'll do a good enough job using your speed (calculated from GPS on the phone) and grade of road (again, GPS).

Get yourself a bike mount for the phone, and go with that. You can even have the data from Strava automatically pushed to MFP as well.

This is *not* perfect, and there's a number of ways that the estimates can be off (GPS glitches, not knowing how fast you're pedaling, not knowing how much force you're applying to the pedals, your phone dying partway through a ride due to the battery getting overly taxed, no heart rate since there's no HRM attached here, etc).

You can improve things by adding in a heart rate monitor, but check https://support.strava.com/hc/en-us/articles/218959288-Heart-Rate-Monitors-that-work-with-Strava for details. If you go with a bluetooth low energy compatible HRM, that's your best bet for maximum ease with the phone, and that will help get the calories much closer to accurate while keeping your total cost under $100 (the HRM should be $60 or less, and the bike mounts are usually $30 or so).

The other stuff can be added more piecemeal if you ever decide you want to add it, but this will get you started and getting some useful data for you to ponder.