Which cassette for new bike

My frame is in for my new road bike and this next week they are going to start building it up. I have to decide the gearing I want and thought I'd see if anyone here had any advice about this particular decision. It's Campagnolo Chorus and I've narrowed it down to either the 12-27or 12-29, both 11 speed. Compact double up front. I currently ride a standard double with an 11-25 older 10 speed Chorus so either one is going to give me a wider range of gear ratios than I have now. At this point, all I can think is that one gives me tighter grouping for smoother shifting and the other gets my two lowest gears a little bit lower, but bigger jumps at that end (23-26-29 as opposed to 23 -25-27). Just wondering if there is anything else to think about before deciding this week. I do not plan to race, but do want to do some faster group rides. it is relatively flat where I ride, with some hillier terrain for organized charity - type rides. Thanks!!

I guess it depends on how you feel on those hillier climbs and how often you do them. Do you feel like you could use a lot of "help" when climbing on your current bike? If so, then maybe you want to go for the 12-29. If not, then the 12-27 is likely fine.
Also, is your new bike significantly lighter than your old bike? If so, that also might make the climbing a little easier too.

Do you ride conservatively or do you occassionally over do it? The reason I ask is...I went with the 29 because I have a tendancy to over do it and, well, having that 29 when the wind is blowing, the road turns up and I'm spent is, for me, a very good thing. That said, it isn't a huge difference, but when I use it, it is nice to have.

In comparing the exact specs of both the 12-27 and 12-29, I'd go with the 12-29. They both have 12, 13, 14, 15, 16, 17, 19 and 21 sprockets and you'll benefit from the tighter spacing on the flats. The differences are at the far end of the cassette and, at that point, I think you'd benefit from a easier, rather than harder, gears when the road gets steep. Either way, I'd expect the shifting, even with the bigger jumps. Campy shifting is always so smooth IME. And remember that you won't have this cassette forever. If you end up wanting the tighter spacing, you can opt for that when you eventually replace the cassette. I'd err on the side of caution at the outset.

It sounds to me like most of your riding you don't need even the 27, but for those organized rides you think you'll want the 29. Why not get an 11-25 or even 11-23 for your normal riding, and the 12-29 for the rare hilly days? It's just a tug on the cassette tool and a tweak of the B-screw, easy peazy.

On my bike with Campy Chorus and a compact double I went with a 13-29, which was available at that time. I loved it, and yes, I did use the lowest gear more than a few times on really big climbs, so I was glad to have it.

Lots of good advice. It's why I asked, as I like to hear other perspectives. I will rarely ride hilly terrain, and I'm afraid to say that I don't "overdo" it as often as I ought to, but having the lower gears might be the right thing to do. I want the biggest bang for my buck, so to say.