Say I have two ad groups. One named - herbal diet pill - and the other named - diet pill reviews. Now say I have a keyword like - herbal diet pill reviews - Which adgroup would make more sense to put it in since the keyword seems to cater to either. Anybody have a method for this? I have many keywords in a campaign like this.
The issue of which adgroup you put it in, or what you name your adgroups is a bit beside the point. The deciding factor is what ad text do you want that keyword to trigger?
Generally, I would agree with Magda but also suggest you consider the landing page and display url you are expecting the keyword to lead to (this is to some extent a 'given' in Magda's reply.) In the sense of language then "herbal diet pill reviews" is clearly about reviews ("reviews" is the noun and "herbal diet pill" the adjectives) and therefore should be in the second of your groups. As a searcher I would expect "herbal diet pill" to take me to a page selling or defining the composition, ingredients, etc of the pills, and "herbal diet pill reviews" to lead to a page of professional or customer reviews of the effects of taking the pills.
If the keyword is generating a lot of impressions and counts for say the top 70% of your business, put it in it's own adgroup named herbal diet pill reviews - in a 'one to one' structure.
Assuming your desire is to sell the herbal diet pills, I would create an advert such as: Herbal Diet Pill Reviews Why Should You Buy Diet Pills? Visit Us For Reviews! which would then lead to a page with reviews and a clear option to buy. As long as keywords like [herbal diet pill reviews] have an advert like this and you meet expectations by landing them on a review page, you will have a good chance of making this keyword work for you.
With regards to the ads, it's test test and test. Split test will in time, make your adgroup perform better and better.
Definitely test using the keyword in each campaign. Speculation is never as good as testing data. Good Luck.
I always keep my title matching the keywords in question, so would definitely say to group your ads with your keywords in each individual adgroup, if that made sense.
You could add your keywords in both ad groups, and test them. Do you think that targeting for them is the same in both of them? It's quite improbable. One of them should be better targeted for your keyword - it's why you created different ad groups, isn't it?