I have not sat on a bike saddle for 10+ years, but I have been camping with a tarp for around 7 years, in all seasons, from +30 to -22 C.
I would say a lot depends on the locations. If you have trees available, then a tarp is in my opinion much more comfortable choice. Bug-net keeps you sane and depending on how you set the tarp up, you can be protected from the winds or be cooled by the airflow under the tarp. I have never been cold nor wet under a tarp.
For winter use, a slow burning long log-fire keeps things nice and comfortable. A proper sleeping gear, of course, is a big bonus.
It takes practice to be able to set tarp up in a fast and effective way. So do expect some learning curve.
A tent for me is a big no. It is claustrophobic and the condensation problems are usually terrible.
But if you are going to sleep in someones backyard or more public places, then a tent provides what tarp can not- privacy.
Tarp will (no matter how much you close it in) always be a more open shelter.