There's no pattern, but there's more value in going forward first and D later, for a few reasons.
Mainly, D's develop slowly when compared to forwards, they are harder to predict and teams seem to put a premium on players that are going to make an impact sooner rather than later. Forwards always go earlier in the draft, unless the defenseman is an absolute stud. Take a peek at prior draft and watch the forwards drafted in the first and the D drafted in the 2nd and try to beat the best combo with a D drafted in the 1st and a forward drafted in the 2nd. It's rarely the case that the latter is the better group.
Guys like Brook, Subban, Josi, Romanov, Weber, etc all go in the 2nd round, while players like Poehling, Kotkaniemi, Barzal, etc usually don't drop to the 2nd.
When you take a peek at the top scoring Ds and Fs. There's 11 forwards that were picked outside the first round in the top 50, 23 in the top 100 vs 23 in the top 50 alone for defenders. Those are pretty compelling numbers, the success rate of D's in the 2nd round or later is basically double. (It goes up to 32 in the next 50 for defenders BTW.)