My experience with Guard is that they're too slow for 7th edition. Even ignoring Maelstrom [I only have one friend that plays them at all, and we typically only play Maelstrom 1/3 or 1/4 games] they're SOoooo much slower than Marines [Bikes and Pods] Eldar, Tau [Sit'n'shoot Tau are for suckas] Dark Eldar, 'Nids, GK... uh... absolutely everyone, really.
The changes to mission setups mean you can't guarantee that you'll have objectives in your deployment zone. If you can't guarantee that, you MUST move out to claim them, and Guard shooting pretty much falls to pieces once you move. Things that don't fall apart, probably don't want to be closer to the opposition than absolutely required. So you wind up in a lose-lose situation where you either build fully mobile armies that are less mobile and less shooty than other codices [with vastly inferior CC] or you accept that a mission may be straight up twice as difficult for you to accomplish because you need to move away from your deployment zone because there aren't any objectives in it. Build an army with some mobile, some sit'n'shoot, and then kick yourself because your defence line with shooty blobs and artillery don't have an objective to hold. Pray that a couple of Vet Squads in Chimera with a Bird and Squad don't receive the entirety of your opponent's firepower / assault [they will] and then just shrug your shoulders because there isn't a powerful strategy in the codex that works in 7th.
They have powerful units, but they don't create win conditions. I have objective secured on my Vets, hooray! Except they get murderated by Thunderwolf Cav, and then the TWC score that objective. Poopers.
We used to be able to anchor an area of the board, to provide cover fire to advancing units. If the advance was squashed, we could still hypothetically hold our own objective/s to make a game of it, trying to kill off key enemy units to deny scoring. That doesn't work anymore.
The trouble with allies, outside of Knights, is that you wind up building a list, then realizing that you'd be better off taking more and more allies, until you don't have any Guard left.
It happened to me. You get in a situation where Guard have good sit'n'shoot, so you use them for that and you use your allies to go out and grab the objectives... but a few games go by, and you realize that the Guard are good at shooting and killing, but really bad at winning the game, so you take a little less, and a little less... and you do better and better until you stop playing them competitively.
I still pull them out sometimes, but it's more for nostalgia's sake. I've tried fully Mech'd, and it worked the best. I take a Valk and Vendetta for mobility / flyer defence. A slow rolling anchor [6" a turn, while my opposition moves 12, then boosts, or assaults, or just flies around] and I fire as I roll. My faster moving opposition flanks me, opens the Chimerae, assaults the dudes and then it's pretty much over. Krak grenades in assault start tearing the asses out of my Russes ['cause they hit rear armour, LOL!] and I usually lose by an objective. If my Valk doesn't get shot down, I tend to be able to get my Vets to an uncontested objective late game, and if the game ends turn 5/6 they have a decent chance to hold on. I've not won a single game that went to turn 7, in 7th edition. Ob Sec means jack amphetamine parrot on Guardsmen. There's no reason to play Battleforged with them, other than it's a habbit and my group frowns on Unbound... for good reason.
If I build my old style of Hybrid lists, I do well if I happen to wind up with an objective in my deployment zone, or Kill points 'cause I just turtle up and hope the game ends turn 5. They aren't as fun to play, because you're always vulnerable. Things are moving so fast now that the cardboard armour on the side of the Chims gets torn up. And then you get shredded in the open. People may hate on bolters, but they still do the business to Guardsmen that get explosively ejected from their rides.
I take a lot of dozer blades, and actively plow through terrain now to get some kind of save for my tanks.
So, as the cool kids say...
TL;DR - Mechanized, with a pair of Flyers, for best results at 1500 to 1850 points.