The process itself is straight forward but I had to work in a really tight space under the sink. That was really what made it a pain in the ass. I had to lay on my back and cram myself underneath the sink in the cabinet to reach everything plus I'm a 6' tall goon so that definitely wasn't helping either. You're just stuck in an awkward and uncomfortable position most of the time.

Same experience installing a dishwasher. Inside a small cavity accessible only by climbing over my new dishwasher and avoiding the existing washing machine, crouching using leg muscles I rarely ever use, with the only light coming from a torch, on flooring made damp from dripping pipes that I hadn't tightened enough, arms getting sore from lifting them above my shoulders for extended periods, I understood why plumbers get paid what they get paid.

Sinks are one of the few areas that I don't think one can get out of using threaded connections on the supply lines (haven't seen push-to-connect for that last leg yet). A lot of them use NPT threads, and NPT is very easy to put together in a way that will have a slow leak. Even a single drop every few minutes can cause big problems if left unattended for long enough. Also, a lot of the connections are in locations that are a headache to reach, even with a basin wrench.

Getting a good seal on a sink drain can be a little tricky the first time too.

The sink supply connections (usually from a shutoff valve) are compression threads (a parallel/straight thread).

If the valve itself is threaded on, that inlet might be NPT (or might be compression), but the valve outlet will be compression, which uses a tapered ferrule to provide the seal and straight threads.

The faucets I've seen are generally NPS where the supply lines attach to the faucet, often with the retaining nuts (or whatever they're called) using the same threads and going on first.

To answer GGP's question, what's difficult about faucets is getting up behind the sink, with your back straddling the corner of the cabinet, reaching up with some sort of basin wrench that inevitably won't grip those bespoke retaining nuts well. Especially removing the old faucet where the retaining nuts are a bit seized.

> The sink supply connections (usually from a shutoff valve) are compression threads

I've seen both compression and NPT. I only have three faucet-replacement data points to work from, but I haven't developed a feeling for why manufacturers will choose NPT in some cases.

Compression fittings are pretty straightforward, IMO. No complaints from me about those.