Have stayed in all hotels you mentioned...each offers something different...someone else mentioned le meridian..its the "cool" hotel with very modern lobby and amenities, smaller rooms but overall a great hotel (but they charge 1500 INR per DAY if you want a dvd player in your room!) Taj Mahal hotel is upscale and club rooms are nice...ITC is literally next to Taj and also very upscale, room size varies by category but service is impeccable (as it is at Taj)...on a personal notel, i prefer ITC (their breakfast buffet is amazing!), but all three (Taj/Meridian/ITC) are within a block of each other and centrally located, clean, safe and 5*...

as for the "luxury tax", this is one of the things you really need to figure into any rate in delhi and in a few other cities in india...you will be charged 12.5% on the RACK rate of the room (unless you use points, in which case its included, but be careful with the SPG cash+points option bc you STILL get charged tax on the rack rate, which at times almost doubles the rate you are paying!)...rack rate at the meridian in november for a standard room was pretty high (I think it was 14,000 or 15,000 INR)...

Also, many SPG phone reps will tell you something different, but the hotel will tell you the truth. if you have a doubt, call them directly...also, for the same reason, beware of the "free" upgrade..you will be hit with the luxury tax on the rack rate of the UPGRADED room at checkout...