Your going to get a million different answers because everyone's experiences, tastes, expectations, etc, from a typewriter will be different.
Which brand consistently made quality machines?
- Olympia; '50s and '60s SM series models are particularly rock-solid. I have a soft spot for the SM2, 3 and especially the mid-'60s SM9.
- Smith-Corona; Late '40s Sterlings, 1950s Silent-Supers and Skyriters are snappy and solid.
- Royal Quiet De Luxe; Late 1940s models make for a pleasant writing experience, despite the 'word-joiner' idiosyncrasy that these models are prone to.
- Remington; I've had a few of them and they were nice to use, but the ribbon arrangement (no spools) made them a hassle. And I'm not a fan of bucket-shaped keys.
All of the machines mentioned above are semi-portables.
Olivetti made nice typewriters. I have an early '80s Lettera 32 (bought it new when I was a teenager) and a circa 1953 Studio. I did have a Lettera 22, which is considered classic, but, like the 32, the typing feel can come across as a little sluggish. Someone once referred to them as being 'filled with mud'. That about sums it up.
I prefer my typewriters to have a snappy feel to them when I write. It's funny, but you really can feel it in your fingertips. This is why I rate the 1950s Smith-Coronas and Olympias so highly.
I've never used an Underwood. Had an Imperial Good Companion 5 for a brief while and it was okay, but I felt the Olympias had the edge.
My Hermes 2000 was an okay machine, but it too had a word-join problem and, since I already had the Royal QDL, I figured one crazy typewriter in the collection was enough.
The Olympia SM9 that I have would probably be my desert island typewriter (assuming I could find paper) because the keys only require a light touch and it has a basket-shift (making for less pressure) as opposed to a heavier carriage-shift. My model was made in late 1966 and I personally think it wasn't used much before I got my mitts on it.

I'm sure others will chime in with their own views based on their own experience. Since you're in the US, you should have no trouble finding a nice Smith-Corona or Royal. Just make sure you have a typewriter repairer handy. Or buy a machine that's been serviced recently.
Best of luck!
 

Ignoring all the caveats rightly mentioned above, let's keep it short:

Standard; Olympia SG1 (2nd choice; Hermes Ambassador)
Portable; Olympia SM9  (2nd choice; Olympia SM4).

Let the games begin...

Ok, beak.
Current favorites are:
1948 Remington Rand Model 5 Deluxe
late 40's Royal Aristocrat
 mid 60's Smith Corona Galaxie 12

Machines I thought I would like but really not so much:
Remington #2 portable
Underwood Noiseless portable

Machines still on the waiting list:
Underwood # 5 (two of these)
Underwood Noiseless Standard
Remington Noiseless Standard
Royal FP
early 40's Smith-Corona Sterling

Machines Already Passed over:
Olympia SM 9
newer, plastic bodied Royal Aristocrat
All digital "typing wedges"

I hesitate to give an opinion on any of these because everyone else likes or dis-likes a particular machine for their own reason and I feel that everyone should be their own judge on something as personal as a typewriter.
I also, am discovering a change in my own opinions as I learn to touch type.
My delightful S-C Galaxie 12 went from number one to something other than one because touch typing is easier on the R R Md. 5 and the Md. 5 has a better touch for me.
I suspect as I become more proficient at touch typing I may become LESS choosy about the machine and better able to compensate for differences between them.

The thrill of the hunt is the thing.....
Once that is over, it's just another steak, potato and salad.....

HABD!!

I think it;s important to remember that we're talking about collecting old machines in whatever condition they happen to be in. Each machine by this stage is likely to have its foibles, and even in the days of yore, one Which? report on typewriters found that touch and performance could vary more from one machine to another than from one  make to another. It's not just shopping! 

Hermes made great machines. As per Rattle Tap's list, my Hermes 2000 is a fantastic, reliable, gorgeous machine to use; I bought it in a shocking condition for £3 and then spent some money on getting it repaired and the platen re-covered. The 3000, though currently priced stratospherically for reasons not to so with typewriters themselves, is also a solid and precise machine to use. Some hate the touch; I love it. 

I've found Olivettis to be predictably reliable. The ones I like the best to use are the bigger ones, the Studio 44 and Lexikon 80. They have a very different touch to the Hermes and are my current favourites. 

Olympias are unassailable, whether you like them or not. I've gone off the SM9 a bit, but it is still a great machine. I love my SM3 but right now am preferring the Olivettis; that's no slur on the SM3!

Optimas were essentially Olympias. 

The Torpedo (or Blue Bird) 18 is a superlative machine. 

I know less about American typewriters but have found the ones I've used on the whole less unmissable than the German and Italian ones, more prone to skipping or bunching (that is, I guess, more sensitive to typing technique, not so much built to compensate). 

And on the whole that's it, though there are other makes one cold mention: Halda/Erika & Groma spring to mind... Most people seem not to like the touch of a Kolibri but I seem to have found a really good one! 

On the whole, the bigger it is, the sturdier and more reliable it will be (Kolibri excepted because it is so heavy, sturdy etc for its size). In my experience, more ultraportables tend to be a bit more trashed than bigger machines, because more of them have been more heavily used. 

After this, it is really down to individual taste as to which machines you prefer personally, and what you have the good luck to come across.

My favorites are a couple of L.C. Smith standards that I have.  As for portables, I have a Royal Futura 800 that I like to use and it was in great shape as found.