I also start with AutoEurope and then compare with direct rentals. I end up almost always using Europcar. Sometimes it's a better deal directly, sometimes better through AutoEurope. You have to been careful with the fine print! Sometimes there are fees included in a direct rental that aren't included in the AutoEurope price.
Twice I rented in Andalucia, twice point-to-point. I didn't compare with returning in the same city because it would have meant wasting time backtracking. Once I went from Jerez to Granada, once Sevilla to Cordoba (not directly :-). The rates were very reasonable.
Where do you want to go on a day trip or overnight from Sevilla? Most are as easy by train, or maybe even easier. Note the hours of the rental agencies. A single day rental may mean leaving the city after 9 am and having to return by late afternoon. If you are planning a night or more between Sevilla and Granada through the hill towns, it makes sense to rent a car (that's why I took a car both times). Otherwise, train and/or bus is usually much better.