Which one will get warmer the fastest...reservoir or lake...???

Being here in California, I would say a lake would warm quicker.  The water would be darker, ie absorb heat better and not as deep as reservoirs.  My guess anyway.....

Around the places I fish here in Kansas, I would say lakes would warm fatser.  The reservoirs are much deeper and most of the lakes have a lot of springs running into them which keeps them alot warmer.  Once late summer gets here though, the lakes are like a hot tub and the fishing really dies down but can be great fishing on the reservoirs.