I would like to comment assuming AVG uses the same engine as Avast Free. I used Avast free for many years despite all the naggings and the privacy invasion, but eventually moved off it because the memory it used kept growing (compared to my web browser, FF, which uses the most memory on my system day-to-day) and I had to reboot every few days. I went to BitDefender which was very nice because of no nagging. This still used the same ballpark of memory although it didn't grow and I didn't have to reboot. I had some concerns related to root certificates, SSD wearing, and because of the trend that all the forums now seem to recommend average users to use MS defender, I am now running MS Defender.
From the memory standpoint, MS Defender is a stunning success compared to the other two. From the "Private Bytes" column of Process Explorer, it always uses around 360-390MB of memory compared to >800MB of the other two (with regular reboot for Avast). My computer also seems to be snappier as well, but this is more marginal. Since I base my "detection performance" from the AV comparatives, they are virtually the same with some slight edges toward Avast and Bitdefender.
I understand from tests published by other people that a full scan for MS defender is significantly slower than Avast/Bitdefender, but I have never run a full scan using MS defender yet because 1) I was regularly running Bitdefender full scan, why run the same thing if it's going to be slow 2) MS defender seems to be picking things up even when I am not running a scan, and I am not using the files that it picks up (WTF), so why run a full scan? Quick scan is faster with MS defender, but this is in the margin of tens of seconds.
Nowadays, with the security habits that they try to instill in you: no funny links, no unexpected downloads, super cautions (VirusTotal) for all expected downloads, no email links, no pirated software, minimizing software/extension used, exclusive control of your computer, scanning devices connected to your computer, I don't see how I would practically ever see the "detection rate" in action personally. Gone are the days of trying out those nice freeware/shareware. Welcome to the days of grandpa's computer. I fear the supply-chain attacks of the existing software the most.
TLDR; I am happy with how MS defender turns out. Avast and Bitdefender had web protection, at the cost of installing root certificates and feeling freaky about them (I don't think Avast even tells you, which was comforting). I do use AdGuard DNS for ad/malware filtering, with more filtering from uBlock origin, trafficlight, and Malwarebyte browser guard. With 32MB of RAM, and better budgets for SSD, I might have continued with Bitdefender. Avast free with its nagging is out (with Avast one free being worse.) I am neck-deep with MS privacy invasion anyway, maybe not adding more with the abilities to read all my encrypted traffic is a good idea.