30 & 38 are low bridge, the rest are probably due to passenger numbers and used where can be best.
Fairly common now, appears every day or two.
Lothian
Central: 1, 7, 8, 10, 11, 12, 14, 15, 16, 19 (evening), 22, 23, 24, 27, 29, 31, 37, 41, 44 (some runs), 47 & 100
Longstone: 3, 25, 30, 33, 34, 35, 36, 38, 44 (most runs), 200, 300 & 400
Marine: 2, 4, 5, 19, 21, 25, 26, 42, 45, 48 & 49
Night services all Central bar the N22, N30, N31 & N40. All express services central bar the X26 at Marine, X33 at Longstone & I believe X37 has shared runs with Marine.
East Coast Buses
Musselburgh: 106, 113, 124, 125, 126, 127, 128, 139, 140, X5, X6, X7, N106, N113 & N124
North Berwick stores some buses after completing services X5, X7, 106 & 124.
Lothian Country
Livingston: 43, 276, 280, X18, X27, X28, N28 & N43
Tours are stored at Marine.
Please correct me if there are any inaccuracies.