Hello Onkarah,
A great question about meditating on Lord Shiva and Lord Vishnu or Lord Krishna. When I meditate on Lord Shiva; I get the sensations of what I have described in my post in the thread "ponder". Lord Shiva is like a Sphatika Shivalinga- clear - Nirguna- He appears exactly as the One which ur mind sees Him as, but in reality He is undescribable. I get vibrations of Bliss, extreme but effortless renunciation, Gyan of the Brahman. Rarely only, I think of Lord Shiva as the "Aghoresh"; even in that form I have had vibrations of a "strictness" but with great Love.
Lord Krishna's meditation starts with the vibrations of love. But beneath all those vibrations if one goes deeper, then u get the feeling of the same Nirgun form of Shri Krishna like Lord Shiva. Whoever fixes their Indriyas with whatever intent on Him; he by the form of Krishna becomes Nirgun himself. Beneath all the leelas of Shri Krishna, if you look deeply, He was an extreme renunciate even though He was a King. Whoever fixed their mind on Shri Krishna with whatever intent, they attained salvation inspite of all their faults or goodness (e.g Gopis who looked at Him as friend etc, Kansa and Putna who looked at Him as enemy.) This the power of the form of Shri Krishna- He is like a tej which destroys all the faults that come in contact with Him and no faults touch Him - He is Nirgun.
In my opinion, "philosphically and empirically" are not very important. Only important is how spiritually it advances a devotee. Lord Krishna's worship starts with love for Him/His leelas and ends with the Gyan and true renunciation. Lord Shiva's devotion starts with some renunciation and Gyan and then as u have a true Bliss of the Lord u develop immense love for Him. Sometimes I consider Lord Krishna and Lord Vishnu as the same "Nirgun Shiva" with a new look and new leelas.
Regards,