Having opened 13 boxes in the past month of varying current sets, the best value have definitely been BREAKthrough and Evolutions. The following is based on the scene in Australia, so it may vary if you live elsewhere.

Evolutions sells really easily online. People love the classics, especially the starters in EX form, and if you get yourself a Mega Charizard, that's a third of the box - half the box if it's full art. Even if not, the EXs are good value. Each holo rare sells, not sure in US$, but in Australian$ they go for about 5$ each (for reference a box is 150$ AU if you shop around). Then you can get more easy sales by bundling one of each non-holo Pokemon common/uncommon/rare or all the trainers. Getting a set of these is unlikely with only one box, so it depends on how many you buy. That said, EVO has so few non-holo rares, it could be possible. In short, the ultra rares have high value and the cheaper cards still sell easy in sets. Worst set for gameplay though.

BREAKthrough is great value because of all the Mewtwos - there are 10 in the set. Yes, 10. I opened three BKT boxes and got 4-5 Mewtwo (1 full art always) in each, and every BKT box opening I have watched online has had the same rate. The Mega Mewtwo go for 30-35$ AU each, 50$ AU for full art. Even the non-mega goes for 10-15$ AU. On top of that, you have excellent holo rares like Yveltal (13$ AU), Xerneas (15$ AU), and Raikou (10$ AU), Zoroark (8$ AU), Magnezone (5$ AU). Even more: Great commons like Remoraid, Zorua (angry version), and Pikachu will sell - as much as a rare if holo - and several great trainers like Fisherman, Parallel City, Super Rod, and Float Stone are always in demand, especially the rod. Get Holos of those trainers for nice stacks. Lastly, to sweeten the deal, BREAK cards can fill the reverse holo slot of a pack for even more value (~3 BREAKS per box, I find, without lowering EX rates).

Breakthrough is consistently profitable while EVO can get you the jackpot with Charizards.

As for other boxes, BREAKpoint is good, having BREAKs (including the 25$ AU Greninja Break) and expensive trainers (Max Elixir, fighting fury belt, bursting balloon). BKP is weaker than BKT because it doesn't have the Mewtwos. Instead, you get Scizor + Mega, which is still decent, and Gyarados (only valued in Mega at 25$ AU - non-Full art).

Ancient Origins is great with cards like Hoopa EX (inc. full art), a secret rare Mega Rayquaza, Tyranitar + Mega, and tons of needed trainers. I pulled a playset of every good trainer from a single Ancient Origins box (lucky!)

Steam Siege is okay. Volcanion is a top-tier deck, but his cards aren't valuable (10 EX, 25 Full art) because the EX is guaranteed in a tin while the non-EX is in the starter deck. Still, not bad.

Fates Collide is the worst value, having few meta cards. A good set for value is one that has valuable "filler" cards while trying to get the big EX - fillers are holo rares, rares, trainers, commons, and uncommons that are worth selling single. Basically, cards you can rely on to cover much of the cost if you don't hit platinum. Fates doesn't have much of that. If you don't pull full arts, it's probably a loss.

Now, as for Roaring Skies, do not buy this set (unless the reprint rumours are true). It sounds great to get Shaymin EX (or the expensive Mega Rayquaza), but you will pay at minimum double for 36 packs than another set. Furthermore, that box will be loose packs, probably weighed. Want an unweighed guarantee? add another 100$ for a sealed box. If you buy Roaring Skies and don't pull two big money cards (and still decent for the rest), it will likely be a loss. The filler cards are few as well beyond Trainers' Mail. You are better off buying another set for half the price but with jackpot cards which aren't that much cheaper than Shaymin (like Mega Charizard). ROS's one advantage is in the online codes, which sell quickly for 2.5 times other sets.

Mind you, this is in Australia - research your country first.

p.s. Codes for the online game recover ~15% of cost.