Starting with what you like....couldn't be better advice.
I love to include "build a carpet layout to keep you happy and inspired, while you build big".
Never had one? Buy and sell off again, or borrow, a..... tin Marx, cheap 0-4-0-ish lionel can motor, Polar express tmcc can motor Berkshire, 6-driver post war, then small, and large diesels with Pulmore and can motors.
Avoid the PW with a plastic motor case till your sure about wanting one. Interesting and fun, but not impressive, or a "starters" train anymore.
Early MTH had such oddball tech issues I still fear the brand. But my brother had all the issues, not me, and he still prefers them. (great Gramps liked Kusan/AMT/Auburn, Gramps liked Lionel and (early) Williams, Brother likes MTH, and I'm growing very fond of Marx after 50+ years of Lionel. Dad fished alone on rainy days
Anyhow all those suggestions are easy on the wallet (bet I could find all of them for under $300 total), all easy to find too. You run those a few hours each, and you will know a whole lot more about your own running tastes, and know if you "need" more tech. a bigger loco, etc., or not.
A smart move might be the older sets that included the TMCC systems. Usually a good price on them, and good locos of those years. Almost get the TMCC free if you compare similar trains being pieced together. The Warhorse comes to mind. A Hudson J, and coal hoppers
The whole hobby has a learning curve but it all begins with what you like. Doesn't mean your tastes won't change as you "mature" either. It may flip flop a number of times during your life. Be prepared to notice before you get too bored!
Whether style, scale, toy, switching cars or looping, PW bullet-proof-ness, or modern tech; work on learning "hands on" about what you really like doing -vs- your perception today, of what you think you will like doing, before you totally empty the bank.. Shows, clubs, stores, and visits to other layouts before you spend a ton, is prudent. Hint, or bluntly ask to man the throttle, many will grin and step back. No fun whitewashing the fences totally alone.
If one mfg. was "hands down; aces" the others would have folded.
I think most of the LC line could be converted to another command system eventually, if you wanted to do it. Sounds would likely need to change with the new boards too. Too many folks are plenty happy with them, don't just ignore them. MTH had a good mid grade line of starter sets with remote unit at one time didn't they?(mentioned?) ("remote", is not always "command")
Not sure? More confused? Low dollar now, means a smarter large purchase later IMO.
Williams is basically modern PW. Bare bones runners, at a good price.
Sounds and remote/ command, aren't my thing. Williams has less $ tied into those things, and I see that as very attractive. The Bacmann/Williams site is normally higher in price as noted by PhillyReading Lee. It's priced that way to help the small shops stay alive, they sell more. Support your local hobby shop before its gone. 30+ years ago you could hardly drive 10 miles (though a town) without seeing a hobby shop. Buy "something" every visit. Even if its paint you don't need, bulbs, or extra smoke fluid. Feed your neighbor. I sense you will, but have to spout the propaganda
Buying a cheap starter set, could get you a weaker loco than you might like. Ask before you leap. Check on the power, not just style. E.G.- for Lionel "car body" (or similar with the "same" general look), EMD or Alco, magnetraction, traction tire, or plain wheel, dual motor or single. At first glance, they look alike to many folks; they aren't.
Although you've mentioned freight, if your going to have a focus based on past eras, vs 70's to modern, I'd suggest at least 1 loco that also pulled some passenger trains. (I like F's, GG-1s, and some medium-large steam for that very reason)
Running passenger trains in the dark, is underrated for a quiet rooms ambiance. The lighted cars are stunning; captivating; elegant; soothing.
Personal opinion, but I think costs, and dollars crying "spend me TODAY" from our pockets, keeps there from being more passenger car sales. Save up; they are sooo nice.
If you have enough experience to know what you like in a loco, spend big on the strongest of the bunch, best options to please the ear, tech to suit ya, and then piece your ideal freight train together as you grow.
Same for power, once you know your place, skip to the best you can afford.
Overkill is seldom a serious regret there.
Just a longer version of many opinions, mileage and post length may vary.