I am a synthetic fan, so I have used Rotella synthetic (now called T6) 5W40 in my 2003 L4330 since its first 50 hr change. It seems to really like it. Easy starts when cold. Engine uses almost NO oil now with about 450 hours on it.
I don't put hundreds of hours a year on my Kubota so I went with Rotella T6. Wally world has it so it's easy to find. I'm not a big synthetic person but for the tractor I did. A few extra bucks for some insurance.