@Luigib, we're all different - some folks find pullups easier than chinups although I'll agree that most find the opposite to be true.
If pullups are your goal, and you can do at least one, I'd just start practicing them as you can, singles GTG is a solid approach.
Some folks, me included, have found that mixing all kinds of pullups is a good way to avoid overtraining injuries. My person mix includes both pullups and chinups on a bar, doing them on the rings where the pullup/chinup distinction kind of disappears, and doing them on uneven rings. I've lately taken to doing them on IronMind's Rolling Thunder handles for an extra grip focus.
When I was training my pullups pretty seriously, the approach I used was to treat chinups as my backoff sets after pullups - chinups were easier for me so it worked out well to do them when I was somewhat fatigued from pullups. E.g., I'd often do a set of pullups, take a relatively short rest and do a set of chinups, then take a longer rest before repeating.
Hope this is helpful to you.
-S-
