There are some on this board who don't like the gas 20 series... and I can't offer an opinion on the gas part, as I've never owned one. You have to decide if gas is something you are comfortable with.
However, we have a diesel 3020, have had it a long time. It's a dependable horse. Not as strong as a 4020, but nimble and runs well.
The downside to a 3020 is good used blocks and crankshafts are in short supply, and re-engining one is not as easy as some other tractors, like say a 2520. Other parts- hyd, trans, clutch are very plentiful.
Good luck in your search.