Proxy shopping is confusing because every provider sorts its catalog differently. You'll see residential, datacenter, ISP and mobile on one page, then rotating, sticky and "premium" on the next. None of it tells you whether it'll work on your target site.
That's usually where people get burned. A scraper runs fine for twenty minutes, then it's CAPTCHAs on every request, and the code gets blamed for what's really a proxy problem.
Here's a better way to sort them. Look at where the IP comes from and how long you get to keep it. Protocol comes a distant third.
Forward or reverse?
These two get mixed up a lot. A forward proxy works for you, the client, and hides your IP from the sites you visit. A reverse proxy sits in front of a server and handles things like load balancing and caching (Nginx and HAProxy are the ones you'll run into most).
When someone sells you "a proxy," it's the forward kind. Pretty much always.
But the reverse kind still affects you. Cloudflare is a reverse proxy, and if you're collecting data from a site behind it, that's the layer scoring your IP's reputation before the page even loads.
Where the IP actually comes from
Datacenter IPs belong to hosting companies like AWS, DigitalOcean or Hetzner. They're fast and cheap. But those address ranges are well known, so a site using something like MaxMind's IP database can spot them almost instantly.
Residential IPs are the opposite trade. They're tied to real home connections from consumer ISPs, so they're harder to flag, but they're slower and you usually pay per gigabyte instead of per IP.
ISP proxies split the difference: the address is registered to a consumer provider, but it runs on datacenter hardware. IPRoyal's article on different types proxy servers goes through how these stack up on speed, price and detection risk, and it's a decent read before you pick a plan.
Then there's mobile. Carriers put hundreds of phones behind one public IP using carrier-grade NAT, so blocking that address means blocking a bunch of real customers too. That's exactly why sites tend to go easy on mobile traffic.
HTTP vs. SOCKS5
HTTP proxies are built for web traffic. With HTTPS, your client sends a CONNECT request and the proxy just opens a tunnel, usually to port 443. MDN's guide to proxy servers and tunneling explains it well, and it also covers the X-Forwarded-For header, which can leak your real IP if the proxy adds it.
SOCKS5 sits lower in the stack and doesn't care what kind of traffic it's moving. It was defined in RFC 1928 back in 1996, supports UDP as well as TCP, and handles IPv6 out of the box (it normally runs on port 1080, for what it's worth).
Does UDP matter? Sometimes a lot. DNS lookups and VoIP both use it, and an HTTP proxy won't carry either one.
For authentication, most providers give you a username and password or IP whitelisting. Whitelisting means no credentials to manage, but it only works from fixed addresses like an office or a server.
Rotating or static
Rotating proxies hand you a new IP on every request, or every few minutes. For something like scraping 50,000 product pages, where no request depends on the last one, that's what you want.
And for anything with a login, it's a mess. Shopping carts and social accounts expect one IP for the whole session, and an IP that changes halfway through looks a lot like account takeover to a fraud system.
That's where static (or sticky) IPs come in. They stay the same for days or months, and if the budget allows, go for dedicated ones over shared, since someone else on a shared IP can get it flagged before you ever touch it.
One last thing worth checking is what the proxy puts in the headers. Transparent proxies, the kind schools and offices often run for filtering, pass your real IP right along, and Wikipedia's page on proxy servers has a good breakdown of transparent vs. anonymous setups.
What's coming next
IPv6 could shake up pricing. There are only about 4.3 billion IPv4 addresses, and that shortage is a big part of why residential IPs cost what they do. IPv6 pools are basically unlimited, though plenty of big sites still treat IPv6 traffic with extra suspicion, so it's not a fix yet.
For now the advice is pretty boring. Figure out what the target site checks first, pick the IP type that gets past it, and only then start comparing prices.