IMO, the best thing is if you have access to an assisted pull up machine or lat pull down.
Bands can work alright (and they're cheap!), but assisted pull ups and/or lat pull down allow you finely tune your progressive overload. The general problem with bands (and spring type resistance in general) is that the non-linear resistance makes it more difficult to judge your progress.
Assisted forms ultimately "assist" you at some fixed point which alters the path you would take if hanging, often removing your core entirely.
Also, I'd take the non-linear resistance of bands over the absence of core activation from a pull-up machine or the very different lat pulldown motion.
For reference, I'm a rounding error away from 50 and I still do advanced bar work - muscle ups, archer pullups, pull overs, etc...
I think it's important to always work with your bodyweight.
80% of strength is neuronal coordination, you'll get strong with the way you train.
Use your bodyweight in closed kinetic chain [1] exercises and avoid the machines unless you're injured or have a specific reason.
There are progressions for every level.
I recommend "Be your own gym" and "Overcoming Gravity" for great references on bodyweight training.
(Also: don't do muscle ups. The only people who like that are sports medicine docs.)
[1] https://en.m.wikipedia.org/wiki/Closed_kinetic_chain_exercis....
To build volume with pullups, complete your sets with negative pullups as gp describes (nb: at least three seconds down from chin over bar to full hang) when you fail the full pull-up (at least two seconds up, from full hang to chin over bar) any more.[1]
>> I am trying to build upper body strength
1. Keep a diary recording every session. 2. Stay away from the bench press. Focus on your back chain, arms, and grip: deadlifts, pullups (weighted, when you can do a set of 20 body weight), and overhead presses. Add squats and weighted press-ups if you insist. (Make sure you get taught both proper form and proper warm-up sequencing and always use them!)
Observe that these are all exercises that most people hate doing. For good reasons: they are hard work, and nearly all the gain is in your back, which you can't see in the mirror.
1. I used to see a lot of people doing what they claimed were pullups, with only a ten inch range of motion. Not helpful in real life. Start from a full hang: shoulders under hands, arms straight.
Also, “make sure you get taught proper form” is doing a lot of work here. It can be hard to find someone who really knows their stuff and pays close enough attention to correct subtle mistakes.
Recommend giving this video a look, and the channel in general. Lots of good vibes and solid advice for working up through a progression without the muscle bro wankery.