Did my valve clearance check at just over 18000 miles, here are the results.

Front cylinder
Ex. In.
28 15
28 15

Rear cylinder
In. Ex.
16 28
19 28

Intakes are on the lose side especially on the rear cylinder, What is better for the 990? Tighten the shim that read 0.19 and keep 0.16 as is?

You're taking the intake cam out to adjust the 0.19, easy enough to adjust the 0.16 at the same time. The cam is out anyway.

Heard and read more than once that the 990 likes the intakes to be on the lose side, wondering if that's true.

Valve clearances are always better at the loose end of the range than the tight end. I've only ever adjusted them if they're outside the tolerance range, and then only to get back to the top end of the range. The 0.16 I'd be inclined to leave as it isn't far out, but I'd reduce the 0.19.

Great, I thought this too.