I think the consensus is: don't convert unless you have a specific award in mind that will be used right away. There are a few exceptions, like if there is a particularly good deal.

If you can get 100k points asap, delta has a promo for 100k transfer with 50% bonus and 25k EQM which would give you their first tier status. That is a great promo and worth hopping on. Only available if it is your first transfer though.

Continental will no longer be MR partner, and the last day to transfer is Sept 30 of this year. Currently Continental and United miles are interchangeable once you link your accounts through UA or CO website. Later this year the programs will be merged and it will just be United Mileage Plus.

So if you think you might want CO or UA miles, wait until Sept 29 or 30 to do it and see if you still want that. The Delta promo would be worth doing now, if you can transfer 100k miles. Otherwise wait until you have something in mind you want to redeem. Bonuses like the delta 50% pop up all the time, so don't worry about losing it.