Well 7th edition has been out for a bit now and while its hard to say exactly how things are going, there are some definite trends. The IG has been doing well, if not on the top, at least what is reported and seen. At the same time, its hard to draw a straight answer, as each of these tournaments has little tweaks and differences that have an affect. What can be said is that IG can be on top, but your going to have to work for it.
My time playing has led me to believe that the IG function best as a combined arms army right now. This is not to say specialized armies (all infantry, tanks etc.) cannot win, they just don't bring as much assets to the table to overcome their weaknesses against some of the strongest armies. Eldar, Space Marines, Knights mixed in, with tau and necrons behind them as well as daemons, are siting at the top and aren't easy armies to budge. Space wolves are here and there is no reason that they will not be fighting at the top as well. In short, there are a lot of strong armies to face and that IG has to be able to beat.
And we can beat them, but its not a straight win either. The best way to really stand in 7th is that you have to be able to defend or win in assault, deal with knights/heavy vehicles/survive massed S6/7 shooting, all the while having mobility to secure objectives.. Leman russes are a great solution to some of these problems, they can deal with the shooting and can take a lot of hits, and their weapons can deal with large variety of targets and even knights if kitted out right. Blob squads are not as good as they once were, now they are still a good unit, but no longer can you rely on the core of your force being them and having a strong chance. Conscripts though are great and pick up some of the old slack and should be strongly considered, not necessarily being must have, but right about there. They can tie so many units up and help you deal with assault, with a commissar or priest, they can hold the line for a very long time.
Wyverns are must take, unless you have a fluff thing against taking them, you really need to take them. They are just that good. Two wyverns are cheap and will help you deal with so many infantry threats. As long as you can pop transports, wyverns will kill what falls out. They also let you spend points on other things so you can deal with heavier threats without having to invest a lot into anti infantry firepower. Add a manticore/basilisk to your army and you now have strong artillery to deal with a lot of different threats. Hydras are also a very strong option, they are cheap flyer defense and can help when facing wave serpents or other skimmer.
When it comes to the infantry, a mix is the best. A platoon with some conscripts and then veterans, with some mounted in chimeras or tauroxes to give mobility. How you kit them out is dependent on you, but I see the regular infantry bring long range shooting, with the vets augmenting close range fire with melta guns or plasma guns. Scions are another strong choice for having some small strike forces that can deep strike with melta guns or plasma or really whatever weapons you want. In Tauroxes they also can do very well.
Bullgryns have grown on me, though if you are going to take them, the formation out of sanctus reach is a must, it makes them so much better. Granting coutner attack and fearless as well as an additional +1 to the cover save of the slab shield, making it a +2 to cover total. Anything in 4+ cover will now have a 2+ as long as those bullgryns are in the way. Add to that they are tough and good in combat and you can start to deal with a multiple range of threats while buffing your army.
The fast attack section is another area that needs some inclusion, with hellhound variants being great choices for augmenting your fire and giving mobile units to go with your transport infantry. The flyers are still a great choice to be used though I would say less is more here. Sentinels are not a must take but are good for many reasons.
The HQs are the final piece, and priests and primaris psykers will remain in many IG lists and should. Add a CCS or yarrick to augment your orders and you can really make great use of your infantry. Tank commanders are also very strong and will bring a lot to the table.
Overall what makes IG strong is its great mix of units and orders. To do well you need to master orders and play and play and get the proper use of them down. With them you can deal with any threat, but misuse them and you will not be effective.
One of the main hindrances of IG armies doing well is the fact that building some of the ideal lists is expensive in time and money. The guard don't just bring one of a thing. Nope you'll have three leman russes, two wyverns, maybe two hydras, a hell hound or two, a vendetta, 70+ infantry, etc. Its just hard to have all the right units, and even I don't have everything for a totally ideal list.
Still though, IG is one of the strongest armies out there and can win against any opponent when played right and the right tools are used. I hope this helps and gives you some ideas. Again, specialized armies can still do good, but have more of a hill to climb and will require very good use by the general.
GG