I had one weekend in Delhi, coming from London, before heading to Bangalore for work, and found Sulekha via TripCrafters. They were the first to reply, had a great proposal for the itinerary, and a very fair price. I was a little nervous about trusting a company without being able to find much about them, but I was very happy in the end. I'd had other offers from other companies but stuck with Sulekha.
I was met in Delhi by Anoj and helped with my luggage, which could be stored in the car in the end (saving left-baggage costs I'd expected). Then we picked up the Delhi guide and went round the main sights. My guide helped with understanding the history and layout of the city and each of the sights, and also gave me some time to explore on my own which was valuable to me, and acted as photographer when necessary. All very good humoured and entertaining. I almost skipped the Chandi Chowk rickshaw as felt it might be a bit 'touristy' but so glad I did it - really atmospheric bustling streets I'd have otherwise missed. We also stopped in a shop where it was the expected hard-sell on some things, but I was happy to buy some gifts even if the prices were higher than you might get elsewhere (I don't actually know), as I was limited on time so happy to pay extra for convenience.
That night I went to Agra with the same driver and slept off some of the jetlag.
Next morning I met the next tour guide, to go to Taj Mahal for sunrise. Really great guide again, very knowledgeable but good-humoured, and gave me time to explore on my own which is really needed here. Then took me to the other sights such as the fort. There was also a stop-off to see marble inlay art and the inevitable hard-sell again, but again I was happy to spend a bit more and be able to bring back for my wife a piece of the Taj Mahal's art.
Downsides? I guess the only thing you could say would be the hard-sell shops, but then (as already said) I actually did want to buy some things and didn't mind paying over the odds which I'm sure I did despite a bit of bargaining. Others with tighter funds or more time available might prefer to spend more time seeing sights and less time being sold stuff, but then on the times I did say to my guide I wasn't interested in a shop he'd proposed, the subject was dropped and we moved on swiftly, so if you're honest about what you do/don't want it should be fine.
Upsides? Good price, really good communication in the build-up (almost instant replies at all times of days to my questions), all staff and guides friendly...can't really think of anything that could have been better for me - was very happy after having been a little nervous before arriving.