shotgun for skeet and pheasant

I guess the best answer is, what type of action do you prefer? Do you like pumps or semi-autos? If you are looking for a pump, definetly the Remington 870 or Mossberg 500. Both are inexpensive, reliable, and overall great guns. I personally prefer the Mossberg between them mostly because I'm left handed and I like the tandem safety on the receiver rather than the cross bolt safety on the 870. If you like a semi-auto, I would agree with the suggestion for the Remington 1100. I own one and I've hunted everything from squirrel to deer with it, and broke several thousand clays with it in my backyard over the nearly 7 years I've had it. It will cost a bit more than a pump, but IMO its the best semi auto on the market for the money. The great gas system also helps reduce felt recoil, good if you're shooting a lot of rounds. I know it doesn't shoot 3" shells, but I've never found that to be a problem when hunting or target shooting, even when shooting turkey or goose. The 1100 is also a little heavier than a pump, but I'm 5'7 and 160 and I can tote it all day with no problems. Extra weight also reduces recoil as compared to the lighter weight of a pump. I don't know if that's a concern for you or not. I've shot pumps and semi autos in both guages and never found any to be beyond what I could handle, but I suppose its different for everyone.
In terms of guage, 12 is the best overall for just about anything you'd be doing, but if you or your friend are new to shooting or shotguns, or are worried about recoil or have weak shoulders, I might sugggest starting with a 20 guage. It will still break targets and can still kill any game animal. I started with one and killed squirrels and some birds with it with no trouble. 16 Guages are a good middle ground but they and their ammo are almost impossible to get these days. I have a Savage semi auto i borrowed from a friend and really enjoyed it but ammo was hard to get and expensive.
As far as choke goes, for trap shooting and any real upland hunting like for pheasant or grouse a normal modified choke is what I would recommend. If you're going to hunt goose or turkey, which are tougher to bring down, you should use Full choke. I have a normal 28" barrel length on my Remington 1100 and have used a same length barrel on a Mossberg 500 20 Ga I used to use.
Any of the above would be great all around choices, you can't really go wrong. As with most gun choices, a lot of it is personal preference. If you can, try borrowing some shotguns from your buddies at the range and try them out. Good luck with your decision.

CZ redhead deluxe 28" barrel

Personally, I prefer a SXS to a stackbarrel.

You should probably haul him down to a store with a large selection and find a gun that fits him pretty good, then tell him to buy that.