Yeah, I would suggest if you have a wooden floor construction (ie. floorboards/sheet on top of floor joists which themselves rest on bearers, which rest on concrete stumps or brick foundations) then a wall shelf is best.
If you have a concrete slab construction then an isolating support is best. Which type depends on what suspension type your t/table has.
Of course, another influencing factor is your nearby environment. Is your concrete slab resting on ground above a subway? (In which case I suggest a Vibraplane is what you need!) Or are you out in the countryside, miles and miles from a freeway? (In which case a sand box or a Mana stand may be sufficient.)
I use a DIY air suspension platform from Steve Rochlin's
www.enjoythemusic.com site. This is a 30lb slab of slate resting on 36 squash balls. It made a great difference to my Linn LP12 - much more base solidity. However, I would use a Vibraplane if I could (my record-storage/hifi cabinet won't take the 90lbs weight!!).
Regards,
Andy