SLR (Single Lens Reflex) is an old form of cameras which use film to form images. SLR cameras offer slightly better quality of color, tone and contrast.
DSLR (Digital Single Lens Reflex) refers to SLR cameras that take digital photos. DSLR cameras are great for budding photographers because they offer live previews and do not waste film when photographers make mistakes. There are more DSLRs available in the market so they tend to be cheaper.
Recommendation: You should buy a DSLR.
Here and also here you can find quick differences between both.