I started myself with a PIC16F84 Back then it was the only cheap uC. All the others still had ceramic packages with windows to be UV erasable, and those packages were expensive.
Didn't like the horrible crippled assembly, so threw it aside quite quickly.
Then AT90S2313 happened. Nice instruction set, Electrical erasable, GCC available and also cheap enough to not care about the price. I had a lot of fun with those, and their bigger brothers (ATMEGA8, 32, 328 and such).
For the last 15 years I started disliking Atmel. Different programming interfaces every 3 year. Incompatible uC families (tinies, later Xmega's) for no apparent reason, and even simple peripherals change each time, which makes it hard to write a "universal" library that "just works" on (slightly) different uC's.
I thought a while of upgrading to the Xmega's, when my uC's became too slow to drive TFT displays, but the XMega's were very different from the Mega's I was used to. I finally settled on Arm Cortex. I went with STM32, but here are lots of others, from the ATSAM, to the LPC.
Just forget about 16 bit uC's. "The market prophets" have been attempting to talk the 8-bitters into obsolescence form the '90-ies to well into this milennium, but they are still going strong. The 8-bitters will stay (Especially when compatibility with a 5V power supply is a bonus). And while the 8-bitters stayed, the 16 bitters never got much traction and have been superseded by the 32 bitters. (Although I think that ARM Thumb instruction set is some kind of mix between 8-bit and 32 bit, but I only program in C and C++ and did not look too closely at the instruction set).
I bought some "blue Pills" with STM32F103C8T6 when those still were real, but those have been pushed out of the market almost completely by the clones, and I have no interest in debugging those. WeAct has some nice breakout (F411 F431 and more) boards you can put onto a Breadboard. I never liked the big Nucleo boards from STM and their integrated programmer (which doubles the cost of the boards). I've been stuck into a "Getting started with STM32" for 10+ years. The complexity of the IC's is one part of it, and I have a hate / love relationship with STM32 Cube (which got renamed at least 3 times in those 10+ years). for STM32 you sort of need it, to set up the clock domains and distribution, and that works. Unfortunately STM is also pushing the "advanced" things. I dislike the HAL, but the LL is pretty acessible and easy to understand. It's a simple compatibility layer just a bit higher then direct register access. I have been porting parts of the LL into my self written Atmega libraries, to make them compatible with both the old Atmega's, and STM32. It "works", but I'm still having doubts whether it's smart to do so.
Another problem with STM32 is the overwhelming amount of data, and their (lack of) organization. There is a very long thread about STM32 and The Cube software on this forum...
I will stick with STM32. Both because the invested time and resources (programmers, development boards) and because lot's of chinese gadgets use them From power supplies to complete PLC's (Yes, STM32 with built in 24V power supply and hardened IO for EUR30) but I'm not too keen on recommending this path to someone else.
The LPC family is apparently much easier to get started with, but I never used it myself. MBed used to be a very nice site to get a market overview of development boards, but now MBed has stopped, I don't know how long that resource will be available.
I also bought some ESP32 boards, and did a few blinking LED projects. The hardware is capable, and it's also popular with hobbyists and hackers (I.e. lost of "getting started" info and tools freely available). But what I really don't like is that the framework compiles a big blob, and then you have to upload MB of data to the thing, which takes far too much time for me. This programming is done many times during a development day, and it gets boring very quickly. A compile and upload cycle for an STM32 is just a few seconds.
Teensy 4 may also be interesting. It has an LPC controller (and is quite fast) and it has a very beginner friendly interface. You can even use "arduino" out of the box with this thing. Con is that it's a relatively expensive board, at around EUR30. I'm not sure how the transition path is from "Teensy 4" to "Bare bones LPC".
Another consideration (for some) is the packaging for the IC's. Those are ever getting smaller, Do you want to (and can you) solder BGA packages? QFN is apparently easier to solder then QFP, but solder joints on a QFP are easier to inspect (under a microscope)
STM32's product range is from small IC's (around EUR1 a piece) up to very big (Hundreds of pins, Megabytes, Ethernet and parallel LCD interfaces). It has a grow path to beyond what I can ever imagine to need from a microcontroller. LPC is also a big family I think, but Espressiv has a quite limited range with just a few models.