I spent a long time working out where to go in Northern India and what was in each location/logistics of getting between each etc. Here are the places I went and the attractions that drew me to them:

Agra – Taj Mahal and Agra Fort
Jaipur – Amber fort, City Palace, Tiger Fort, Jal Mahal and many more
Udaipur – Lake Palaces, City Palace and more a short journey away

My thoughts on each one are;

Agra
It’s worth going to Agra just to see the Taj. Agra Fort is also nice but you could easily see both in one day and there’s not much else to do in Agra therefore it’s worth just arriving for one evening, looking around the next day then moving on.

Where I stayed – Zostel Hostel. India’s first chain of hostels. It was clean, nice, sociableand walking distance to the Taj.
Distance from Dehli – Approx 3 hours by train or 5 hours by car

Jaipur
The Amber fort is pretty amazing and will take a good few hours to look round properly. The view from up by Tiger Fort is also worth seeing (you’ll need to take a tuk tuk). City Palace was ok, it has some beautiful architecture but also a textiles museum and armoury section which is where they started to lose us.
There is a bazaar that’s really good for clothes shopping, definitely worth bargaining there as the prices do start at really inflated amounts and will drop a lot as soon as you say you’re going to look around.
It was great to be in a bigger city for a couple of days, the only thing I wasn’t so keen on about Jaipur was that it’s so big you kind of have to get a Tuk Tuk everywhere and I much prefer being able to walk.

Where I stayed – The Heritage Palace Hotel. We though we’d treat ourselves. Aside from there being an amazing shower I would not recommend going there. It was noisier and harder to get a nights sleep than any hostel I’ve ever stayed in due to inconsiderate guests, unattentive staff (in not bothering to tell the inconsiderate guests to shut up) and doors which beep constantly like an alarm clock if left even slightly ajar, something which most of the guests chose to do throughout the night for some unknown reason.
On our way back from Udiapur we spent one more night in Jaipur which we spent at Zostel and whilst probably my least favourite of the 3 Zostels we stayed in it was still much better than the expensive hotel
Distance from Agra – Approx 5 and a half hours by train

Udaipur
Branching slightly out of the golden triangle but my favourite out of the places we visited in this part of the trip by far as it was sunny, had nice views and was a good place to relax. It was easy to wonder around the town and felt pretty safe to do so.

Where I stayed – Zostel Hostel. Amazing views. We had a private room for one night which felt like being in a hotel with a lake view from our room. Roof top restaurant looking out over the lake palaces (in particular the one that featured in a bond film). They couldn’t have got a better location. Only downside is the restaurant charges corking fees if you want to drink anything from outside, rather than bought from the restaurant and that is the only common area there.

Distance from Jaipur – Approx 7 and a half hours by train or 7 hours by car

After Udaipur we went back to Jaipur as we both had flights going on from there. My flight was to Rishikesh and I had to leave on that date but if I’d had more time I would have loved to have seen Jaisalmer which is known for taking camel rides into the desert and camping there.