Low Humidity and high temp or high humidity and low temp?

27°c would be best at 75% humidity. 29°c would be best at 75%-80%. 28°c is the max I would put your temp.

Both of those scenarios are bad. A vapor pressure deficit chart will tell you what the best humidity is for any given temp. Warmer air can hold more water than cold air so the humidity has to be higher.

Whichever is most consistent in the long run right now the first one. Pot does just fine, and I mean thrives, at 50% -ish. From seed to stoned in fact lol Sure if you can get the temp and RH right do it but unless you fall below 30% or cause a fungus RH is not a stress point. Temp on the other hand that second is high-ish.

At your stage it's better to have 27°C and 80% RH because the plants needs a high RH during the 2 first weeks and then you can go with the second value aka 29°C and 60% RH. Cannabis best temps range is between 21°C and 29°C and I would say the perfect value is between 25°C and 27°C. Don't worry about the humidifier with these values are they are good for differents stage of the veg as 80% RH is good during the 2 first weeks then 60% will be enough for the end of the veg but it's better to not shocking them by switching brutally from 80% to 60%