New HAL Components - Best Practice

I am new to LinuxCNC, but I play a software engineer in life.  I have identified a few areas where new or updated (and refactored) components could be beneficial.  What is the current best practice to build HAL components?  I would assume halcompile, but more specifically, .comp files or just long-hand .c?  The components that I am currently thinking about are in the user-space.   The first one I want to tackle is an updated/new hy_gt vfd component.  I am running 2.9, so backward compatibility is not a personal concern for me, but maybe people don't update?

Any feedback would be appreciated.
Thanks
 

I think you should use halcompile because this also lets you document your component via a man entry and the web site in the same file.
For new contributions, you should be using 2.10 (master) branch as 2.9 is frozen.
Using C would just add extra work. Not sure on user space comps though. I have never written one.

Thanks

If I build against 2.10, how is backwards compatibility handled? I am running 2.9.