They're both good places; the rivalry talk you hear is much the same as you'll read on the "Dallas versus Houston" threads in the Texas forum. I prefer Tulsa, but that's because I'm more into the geography and general feel of the city. But to be honest, OkC has more going for it in certain areas. For example, Tulsa's downtown doesn't have near as much activity going on as OkC, but they're working to change that. Tulsa has a tad more of an East coast feel about it (IMO) and OkC has more of a Southwestern flair.
There is a reason for that; when Tulsa was booming in the 30s the rich oil men from the East coast wanted to make Tulsa into the Philadelphia of the Southwest/Lower Midwest. They invested huge sums of money into the infrastructure and essentially built up Tulsa into more of a cultural city.
Those days are long gone but Tulsa still has that feel about it due to all of the buildings, art museums, and so on. But, OkC is bigger and has more development going on these days. Tulsa kind of rested on it's laurels so long as being sometimes called on of America's most beautiful cities and such that they really just didn't invest much in the infrastructure or try to attract any new business. As a result, they fell behind in the current development boom going on across America and more specifically in Oklahoma.
But, Tulsa is trying to improve things. In the last couple of years, the voters in Tulsa approved a program called Vision2025 (
Welcome) that is pumping new life into the city with a new, fabulous state of the art arena downtown (do a search on BoK arena), improvements to the roads, and a slew of other development in the city and county.