RAM speed above 2666mhz on the Intel system is overclocking since the spec is only 2666mhz, so you’d need a Z490 motherboard to support faster RAM.
The only reason this is something to consider, and this is a small overall difference for an end-user who isn’t tech-savvy, is that the Ryzen 3 3100 can use faster ram in a less expensive motherboard. It being able to be overclocked itself isn’t really that useful for people not interested in that type of manual tweaking.
The big issue here is that Ryzen 3 3100 is presently overpriced at $130. It should be around $100, like the i3.
I made the point of i3 on a Z490 motherboard, because in order to get the closest to the Ryzen 3 3100, it needs to be on a Z490 motherboard to have access to faster memory.
i3-10100F is appropriately priced at $100
Ryzen 3 3100 is overpriced at $130, but that is offset by the lower cost of the motherboard.
i5-10400 is appropriately priced at $179
Ryzen 5 3600 is overpriced at $229, but that is somewhat offset by the lower cost of the motherboard. (seems this is back to $199, which is kinda okay being a year old product but still MSRP)
The i5 has the same issue; will run at 2666mhz RAM on non-Z boards.
The current pricing of Ryzen CPUs doesn’t make them bad, but they are less value than they were just 3-4 months ago, when you could get a Ryzen 3 3100 for $100 and a Ryzen 5 3600 for $179.
At the end of the day, the difference isn’t huge, and if you aren’t really chasing the best performance/enjoy tweaking, getting the cheapest option makes the most sense really.