Before you jump in, you should establish why you want to get back into
40k: is it because you enjoy the models, do you want to play casually with friends, or do you want to play to win?
If your goal is to play to win,
40k is a not a well-balanced game. Check out house rules of wherever it is you're playing, do your research, and build a min-max army that abuses the rules to the maximum extent possible.
If you want to play casually, figure out what army you identify with, and start from there.
If you just want to paint cool stuff and don't have a strong bias towards one army or another, take a look at what gives the best value in terms of miniatures per dollar.
If value is your concern, Space Marines have the huge (the largest) variation of models are the easiest to mix, match and build on a "budget". There are and always will be box sets that give you a good mix for the price you pay. Imperial Guard (Astra Millitarum) have relatively tiny sections in the hobby shop, and there is no cheap way to acquire neat "must-have" units like Militarum Tempestus ($40 for 5 units). In comparison, there are many ways to get Terminators in box sets. Or, compare with Dark Eldar where you can pick up 10 Hellions, Kabalite, or Wyches in boxes of 10 for under $40. Even the vehicles are a lot cheaper.
On the box sets, I look at four things: cost per model, how interested I am in both armies, the quality of the models, and whether I want or will use the special models (like the Ravenwing, Turmiel, Balthasar, etc.). These are a GREAT value, dollar-per-point-pointwise, but a lousy value if you're going to leave them in a box.
If any of your hobby stores still have it, Stormclaw was an awesome boxed set (I bought 3!). Off the top of my head you'll add 2700-point-ish (maybe more?) to each of your Space Wolves and Ork collections, but the really amazing thing is that everything in the box is a proper multipart plastic rather than pushfit -- meaning that you have your choice of torsos, heads, arms, weapons, and so on. You can have choose to outfit all of your marines with helmets, or heads; your terminator can have lightning claws or an assault cannon. In comparison, Dark Vengeance gives you no option as to what units have equipped; so the beautiful sergeant miniature and one of the terminators will always have a chainsword, even though there is zero reason to equip one.
The casts for Stormclaw are also highly detailed, much more so than Dark Vengeance, and I personally think Orks are more fun to paint and play than Chaos.
That being said, Stormclaw has a sticker price of $150 (my hobby shop sold it for $112), and
DV I think is closer to $120 sticker; the old 6th edition
DV has exactly the same models and is usually less than $100. And, of course, Stormclaw is a bit hard to find now.
The upcoming Space Hulk gives you some awesome miniatures for $150; they are pushfit, but gorgeous sculpts. Point-value-wise, they're huge (35 models, I think, including 11 terminators and a librarian), but you can't directly insert them into an army, because they're not configured correctly for two squads. It's close, though.
Personally, I no longer play
40k, but I paint them and collect the models, and still try to build them in a playable -- or at least coherent looking -- armies