RN
The protocol has one property that determines everything about using it, and most guides bury it under a feature comparison: to receive a piece of a file from someone, you must first tell them where to send it.
That is not a privacy failure in an implementation. It is the mechanism. A swarm is a list of addresses, every participant holds a copy of that list, and joining means adding yourself to it. Anyone in the swarm — including someone who joined only to write the list down — can see who else is there and what they are exchanging.
Everything else about client selection is small compared to that.
What the client actually decides
Given the above, it is worth being precise about what a client does and does not control.
It controls how you connect: whether traffic is bound to a specific network interface, whether connections are attempted when that interface goes away, whether the protocol header is obfuscated, and whether the client will still talk to peers if your intended route drops.
It controls what you announce: how long you keep seeding, whether you participate in the distributed peer-discovery mechanisms as well as the tracker, and whether you advertise your client version and, on some setups, your local hostname.
It controls what runs on your machine: the codebase, its update channel, whether it ships extras you did not ask for, and whether it opens anything network-facing beyond what the protocol needs.
It does not control who is watching the swarm, and no setting inside it changes that.
The four settings that matter
Interface binding. The important one. A client bound to a specific network interface stops sending traffic entirely if that interface disappears, rather than silently continuing over the default route. Anything without this is one dropped connection away from behaving in a way you did not intend, and the failure is invisible until afterwards.
Seed limits. Seeding continues after the download completes, which is the point of the protocol and also the period when you are most visible for the longest. Whether that is a consideration is yours to weigh, but it should be a decision rather than a default you never looked at.
Peer-discovery options. Distributed hash tables, peer exchange and local discovery all widen the set of parties who learn you are in the swarm, sometimes including devices on your own network. They are on by default in most clients.
Where files land. Adult material downloaded to a default folder that is indexed by a system search tool, synced to a cloud drive, or scanned by a media library will appear in places you did not put it. This is the failure people actually experience, and it has nothing to do with the protocol.
How to judge a client without a ranking
Client rankings age badly, because the interesting facts about them are ownership, funding and bundling behaviour — all of which have changed for most of the major ones at least once. So rather than a list:
- Is it open source with a visible repository? You will not read it. Other people do, and that is the point.
- How is it funded? Free software with no funding model, a large user base and commercial hosting costs is being paid for somehow. Historically that has meant bundled installers and advertising in the interface, and it has meant it for some very widely recommended clients.
- Does the installer offer you anything? An installer with optional extras has told you what kind of product it is.
- Is it packaged by your operating system's own repository? If so, that is generally the version to take, because the packaging is a second set of eyes.
- Does it have interface binding? Back to the top of the list. If not, nothing else about it matters much.
The part that is not about clients
A client is a transfer tool. The two decisions that actually shape the experience are made before it opens: where the file came from, and what network you are on.
The directory maintains lists of torrent sites for the first and VPN services for the second, and there is a separate direct download section for people whose actual requirement is a file rather than a protocol — which, for a single video, it usually is.