In short - it depends on what you plan to do during your stay. During last years I have stayed several times at Hilton KL and now for about a week in DT KL. I would say that if you are going to get first overall impressions about Kuala Lumpur and surroundings, to order individual guided tours, to attend some temples, to go somewhere on a train etc. than I would probably choose old good Hilton KL.
But if you want to do some non-supervised shopping, to go around on your own in-and-out of the hotel, to use public transportation system, to mix into day and night life of a big town - then DT might be preferrable. Certainly this is very oversimplified, just tried to show the difference (in my subjective view).
DT Lounge staff is very friendly and helpful, no exaggeration there. Just talk to them if you have any question or problem. I always received perfect answers and explanations (special thanks to Priya). For example, I asked about computer and electronics store Plaza Low Yat. While I was still sipping my double espresso coffee, she was back with individually prepared for me and printed (!) paper which contained everything I might need - precise name of store, address, tel. and fax no., operating hours, how to get there from DT. In addition, there was information about two more stores nearby (like, if you already will be there...), plus map with all these places marked on it, and related Rapid Transport stations as well. I was really impressed
Food and drinks in the lounge were maybe not that impressive. I mean, nothing comparable to Conrad Bangkok
The choice however was slightly better in Hilton KL. But DT lounge also has quite decent breakfast. Certainly Makan Kitchen buffet in DT has orders of magnitude better choices for breakfast, and even more for dinner. Beverages in both Hilton and DT lounges are available for about two hours in the evening, some light food is also served. In Hilton there are more choices for drinks and food, but anyway in both places you will have to ask some lounge warden each time to get a drink. When lounge gets crowded, it can take some time. No booze menu in DT
you have to ask and be prepared to receive apologies instead of, for example, cognac. I was able to get red wine, white wine, whiskey.
About construction site: there is indeed one right nearby the DoubleTree. However in my room I didn't hear any noise. Probably because my room and window was on the opposite side of building. At least, it should be possible to ask for less noisy room at checkin.
Generally it was nice stay for me. And first time in my life - New Year in Asia