for gentle or general use I like tool stations "no nonsese degreaser" it's £6 for 5 ltrs and can be used neat, or a very small amount added to water for cleaning floors etc. I've used it on neglected bikes to clean the gritty grime around the chain/sprocket area and around the frame/swingarm in that area too.
It is a gentle one and of the soapy, rinse away variety, so it wont melt though 1/4" thick grease in one pass, but with minimal effort it removes thick grease and grime without smearing it about. I've also used it for cleaning oil spots off my drive by putting it in the addative tank on my jet washer.
It's strength is its gentle nature, you could use it anywhere, delicate paintwork that spirits may damage, etc.
That aside, I generally use paraffin or white spirit, I have brake cleaner, but I tend to use it for cleaning brakes as its quite harsh.