If the player is good enough already and has a big game like a DE with a bunch of sacks or a WR you can go from buying quick development one week to superstar the next sometimes.
Your players certainly progress the fastest if you just focus on the development trait.
For my fantasy draft team the first thing I did was bring up everyone's consistency, then key skills like PMV/FMV/BSH for pass rushers, then a little bit of PRC/AWR, then the development.
Sometimes when I hit quick I'll continue to boost skills a little bit before getting superstar.
It's really up to you.
I'm in the offseason of my first year of my fantasy draft team, and some guys I had enough to take them from normal to quick development, but because it's the offseason I can change their position, so I'm moving MLB Daryl Washington to OLB to upgrade his pass rush moves, then moving him back to MLB, and upgrading OLB Alec Ogletrees pass rush moves and moving him to MLB (I'm converting to a 3-4)
I'll be able to upgrade their development during the season but not their pass rush moves since they'll be stuck at MLB.
It may take a while to get them to the development but at this point after upgrading for a season I don't really need to get them anything else until I get development.
The "cheapest" way might be to get development right away, but some players might take forever to get there.
Upgrading your stats increases your chance of making plays, which gets you XP.
My backup OL barely played any snaps but all made the pro bowl. They're all hitting quick development now but probably should be at superstar. since they never even play i could have just waited to upgrade their stats until they were superstar.