What would you upgrade first

What is more important to you

Depends on current players. If you're just starting, Priority would be getting WR/CB/Safety to 89-90 at minimum since they’re cheap now. 
 

Also defense is mostly a bust this year unless you run cheese blitzes or drop 8 in coverage

Give me offense all day. Defense doesn't exist, nor has it existed in Madden for years now.

I typically try to upgrade my offense when I'm first starting out. You're not going to win many games if you can't score

That said once I feel my offense is good enough I usually tend to focus on defense because I need all the help I can get there

Offense is much better to upgrade since it matters alot more, try playing with a bad defense and ya it sucks but doable if you’re good, try playing with a bad offense and yeeeeeeesh you’re screwed