Even without the intent of GP generation, it's still scientists for me. 3.25 raw beakers (assuming running through a Library) is really decent early on - that's more than a non-river or non-FIN Hamlet, and it's always there so long as the scientist is hired, meaning it has more impact in economic stress situations where 3c on a tile isn't always equivalent to 3 science, since you have to use it for gold on other turns. I have used Library scientists to churn ahead to Aes or Alpha many times while crashing the economy with REX.
You can also get this equivalent of a 3.25c/0f/0h at 100% slider tile with only a food surplus (or not, it is possible to run them while shrinking) and don't actually need a tile to develop for it unlike a cottage, and of course you don't need to invest the time to grow it -- I often shut off scientists in cities once the task of either getting to Alpha/Currency or generating that city's one GS is done.
Early Rep through Mids only makes it better, and it's part of the reason CRE is a nice trait too (start those Libraries a little earlier).
I have run Engineers and Priests before too, when needing just a little more productive oomph. Priest especially are nifty as they give raw gold too, and are easy specialists to spam in a Rep gambit since temples can be stacked and are accessed early. Those situations tend to be less regular though, like when playing Egypt or if I got Angkor Wat.
