I have had two agents in my life, plus an almost-third who although she never represented me was always willing to consider my MSS (a most courteous and considerate lady now sadly lost to us, though from her death has sprung, phoenix like, a remarkable and thought-provoking book by her devastated husband). I also had a further half-agent, but more of him later.
My first agent was outstanding and it was entirely thanks to her that one happy happy day I stood outside Foyles and looked and looked and looked again at my humble little creation waving back to me through the window of London’s most important independent book seller.
My second agent some years later was useless. Months past and still she would not tell me to which publishers she had offered my MS. After a year, I had to sack her: I discovered that she had offered my MS to just one publishing house and, when they had shown no interest, left it mouldering on the shelf for the following eleven months. All that time I had thought I had representation I had not. I realised then that she had been going around hoovering up all the new kids on the block, giving them about fifteen minutes of her time and then spitting them out if no publisher quickly snapped up their work.
The lesson I learnt from those two was this. The one who was outstanding ran a very small two-person agency: because she was growing her business she put in a major effort for me. The one who was useless headed-up a major agency with very big clients: compared to them, I was just an also-ran.
And what of the half-agent? He was a very strange man, semi-retired, who agreed to represent me but only if I made some changes to my MS. Specifically, he objected to the route three of my characters took from Paris to the Bay of Biscay and, more significantly, for some unknown reason he wanted the first-person narrator named, something I had purposely avoided to help readers of whatever background to bond with the story.
Very reluctantly I made the changes (though I confess I subverted his intent by only naming the narrator in the very first sentence, and that sentence was just three words long and the very famous opening of a book covering the same topic). Perhaps because of my thinly-disguised sarcasm in those first words, after all my efforts he declined to represent me. Later I came to realise that he had only ever been on a power-trip: it just entertained him to see how many hoops he could get me to jump through in my desperation to find a new agent.
So my warning to those today approaching agents is caveat emptor. There are some very good ones out there, but there are also some horrors.
Now at this point I was going to write that you should always go with the small unimportant agent just establishing her business in preference to one of the big names. But sadly I then realised that this is not necessarily true, for the lovely lady I mentioned in the first paragraph actually headed-up a major agency and was a very significant figure in the industry. So, sorry: I have no rule-of-thumb to offer. Just be careful out there.