If I were able to take a free straddle UTG meaning I can still fold without putting any money in the pot if I wanted to, I'd take it probably every single time. That way, I would be able to squeeze whenever I had a decent hand or encountered a situation ripe for squeezing with relatively no penalty or I can get a great value hand and raise an inflated pot for even bigger profits
So yeah, if you can straddle for free with no penalty and fold if you like when action got back to you, then take that Rock 100% of the time
BUt if you have to put in a limp or any money in when you have the rock, then don't do it.
As far as button straddles go, you can make the case that its profitable to raise almost ATC on the button provided you have the right image and your table is weak. I would say a BTN straddle is probably close enough to 0EV where you can do it provided you have a strong image, preferably right after you've taken down a big pot and showed down a monster.
I'd also be more prone to do a BTN straddle if I were over 200bb+ deep and there were a couple of mouthbreathing droolers or marks at the table that were likewise 200bb+ deep and I had a strong image and great reads on my villains' post flop tendencies and was able to float/steal a lot post flop.
Otherwise, I'd pass on the BTN straddle.