"Top tier" phones are usually the manufacturer's most expensive line, as long as you stick to the major manufacturers. (I'm sure there's some Chinese company all ready to release a "Note 9", running on some old MediaTek chip, with 16GB of storage and a pen that doesn't work, for $300, so it's not just the name that matters.)
If you want a phone at least as good as an iPhone X, stay with Samsung, Motorola, LG, or even Google (the Pixel 3 is about to come out, so if you wait you can probably get a good price on the Pixel 2 or the 2 XL - and they're good phones).
Going down from there, you have Sony, HTC, Huawei, Lenovo, Xiaomi, OnePlus as sort of "second tier". (Even though "Motorola" phones are made by Lenovo.)
Third tier would be Nokia, Microsoft, Xiaomi, Acer, Asus, Oppo, Meizu, Alcatel, ZTE, Toshiba, Micromax and BLU. (None of these are in any particular order - it's the order they're listed in at gsmarena.) And yes, Moicrosoft/Nokia (MS bought Nokia) would be a 3rd tier phone today.
The top tier is going to be expensive, but so is an iPhone.