I use trays. I'll JOBO tank develop my 4x5" or 9x12cm films occasionally - especially if I have lots of them - but mostly I develop in trays. By inspection. All sizes: 9x12, 4x5", 5x7", 13x18, 18x24.
Unlike may others I prefer trays that are not a lot larger than the film, this gives me better control over the slippery little b*stards. So 9x12 to 13x18 goes in 13x18 trays, the 18x24 in 8x10" trays.