I put a 1 TB HGST HDD in my late '08 MacBook. A larger/faster drive uses more power but I use my MacBook in clamshell mode as a desktop computer so it is seldom unplugged. I read the reviews at the time and HGST seemed to be one of the better brands. I went with a HDD because I wanted the larger storage and a SSD of that size would be expensive for an 8 year old computer. 7200 rpm offers a bit of a speed boost over the stock 5400 rpm drive.
There are all kinds of options out there including replacing your drive with a SDD for maximum speed boost, having both a SSD and HDD by moving your optical drive to an external enclosure, or installing a fusion drive which has both SDD and HDD components. A good place to start with this kind of thing is OWC = Macsales.com which outlines the different options. I also decided not to buy a SDD for various technical limitations such as which models support which bus speeds, and wanting a large, affordable drive. With my 1TB drive I am not sure I notice a huge difference between my wife's newer MacBook Pro with her SSD and mine, but I did notice a faster boot up time.
The hard drive is easy to replace but you will need a #6 (double check me on this) Torx screwdriver as well as a really small (#000 ?) Phillips screwdriver.