They're the tits. Public trackers are literal trash by comparison. Like comparing Notre Dame to a busted gas station chapel in Missouri.

Edit: Don't PM me and beg for invites... Not a chance.

TL;DR: Great to have if you're looking for less popular content, high quality files, and/or are concerned about copyright notices, but the rules that keep the niche content alive make them less appealing for super popular content.
I randomly made friends IRL about a year ago and got an invite to BTN & PTP. I don't watch/download a lot of movies, so my account at PTP has lapsed, but I've kept my account with BTN.
From my recent searches, BTN tends to have higher quality files and more seeders than public trackers, but since a) I have a seed box, which provides a line of defense against copyright notices, and is only strengthened my my *aars (gets me in & out of the swarm before the studios find it), b) I usually can't tell the difference in quality from the devices I'm using (and my friends/family most definitely don't notice/care), c) seed ratio or time doesn't impact access to public trackers, and d) I prefer to keep public torrents alive, I usually lean towards public trackers, and only use the private trackers for things that are harder to find and/or things I want in high quality.
I still try to seed to a minimum ratio of 3.0 on popular files (public or private), and ∞ for more niche files, but sometimes demand is so low, and I need to move files off of my seed box. While a ratio below 1.0 makes me feel "stuck" no matter where I got the file from, private tracker rules definitely amplify that feeling.

I've never liked them outside of the niches the private trackers I had access to were about.

I've had one that sucked for anything other than music (and even the music was annoying because the uploaders had boners for FLAC and this was back when file size still mattered and FLACs are fucking huge and don't sound different enough to warrant the file size), one that only hosted textbooks for college courses, and another that was strictly niche as fuck films that nobody has ever even really heard of.

It's good to filter out bad actors uploading viruses, but it also limits how much stuff is there period.

I switched to only private trackers 5 or 6 years ago and haven't looked back.

I've never really used them as most content I can find readily available on public sites. I do want to get access to the World Boxing Video Archive one day as that is an area that seems to be pretty barren on public sites, unfortunately it seems that the registration is forever locked. Maybe I'm wrong but they all seem pretty pointless unless you have some pretty niche tastes in which case they can make a whole lot of sense.

I do use private trackers but only if I can't find something on public trackers

I don't use private trackers..

ITT: the sourest of grapes.

id like to get into one, I have good seed ratios, just hard to know where to start

They’re basically the RC Cola of Usenet. Instead of messing around with torrents and private trackers, just move on to the grownup option.

Better quality releases and more active users with much less leeches as they get thrown out.
Though there are many site admins with some complex here too.. your experience can vary.

And of course you need to contribute to the community, most trackers will grant you buffer for both uploading and keeping the torrent running. You want something, then you have to give back.
If the tracker doesnt give possebilities to build your buffer in multiple ways, other than just uploading, its usually a shit tracker.
And some are just super hard to impossible to get into. Start small, wait for open signups or just go to new trackers, they might get bigger over time.
Dont publicly beg for invites, you can humiliate yourself in private chats if you are into that.

I've been using private trackers since demonoid. Maybe I'm just a different generation, but I enjoy sharing stuff from my local library on private trackers. Torrents rarely fully die on private trackers. People will generally reseed if they have the ability. I can quality shop, and get things that are generally harder to find/request things that I can't find anywhere.