Firstly, welcome to FT, campertondilo. Because your BLR flight is in the afternoon, and because it is a Friday, I would seriously consider staying at Radisson as the preferred option. One, you can catch up better with sleep and adjust for time zones. Yes, best to prearrange transport, particularly airport to hotel...touts don't really care whether you're a single female...but it gives them added incentive. Staying at Radisson means you can leave at around 1.30 or even 2.00 pm, for your domestic flight.

However, if it is your first time to DEL and/or you want a quick dekko around, then yes, you could stay in the city, but make sure you leave for the airport no later than 12.30 pm. The early afternoon traffic can be unpredictable, and the fact that its a Friday just adds to that.