IMO it's hard to beat a muffler modded Echo 590 for a budget 1 saw plan. Mine is nearly 3 years old, been beat to hell and back, and it still runs flawlessly, I've never had to do anything to it besides basic maintenance. Great power on a 20" bar in my conditions (mostly mixed Texas hardwoods, there's some pine in there too) and a 24" is no problem if you're not in a rush, bulletproof design, never fails to run from below 0° to 110°.
I've ran a friends 400C and it's an objectively superior saw, but it's over $1100 after tax in my area vs under $500 for a 590. If money isn't a problem, you can't beat the 400C. Crazy powerful for the weight, super smooth in the hands, light, I can't complain a bit. I don't know why it's already being replaced after only a few years, seems like a bad move for Stihl.