Good info so far. I'd add that that your federal pension DOES get cost of living, but SOL is correct about the erosion. The COL doesn't start until you hit 62 I believe. Also for CT and OT, don't expect actual time and a half depending on your salary. If I recall, it gets calculated as 1.5x the wage of a GS 10 step 1, or your current wage, whichever is higher.
As for CT vs OT, it's really a matter of whether you want that leave buffer in case you have low annual leave.
Note that travel comp is different and you should use this leave because it doesn't pay out.
For sick leave, it was rightly pointed out that this acts as your short term disability. If you have kids, you'll have a lot more use for it, but don't hoard it for the purposes of added pension, as you'll be leaving workforce early and won't get benefit. If you do come back though after leaving, it is reinstated.
Ricksun