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
 

Both is fine.
The .comp format is more compact and easier to understand and maintain particularly for people not totally familiar with pure c.

Note that the component should remain compatible with older configurations.

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.

Just recompile it.