Garden design is a very personal thing, what works for one person would be a nightmare for another, so whether you want a large tiered fountain or a small pot feature its a personal thing, the only thing I would say it to enjoy whatever type you buy.
There are however some things to keep in mind that are common to all types of fountains and water features.
One thing to consider is how large the space is, this is not to say that large gardens always need large fountains and small gardens need small fountains but rather that fountains are an integral part of your garden design and so you need to consider how you want to incorperate your fountain or water feature, some examples would be to provide a focal point to a planting scheme, perhaps to provide a backdrop to your garden seating or barbeque area, perhaps you are close to a busy road and wish to drown out traffic noise.
If you have a large garden the temptation may be to go for a large garden fountain but this can very often end up as an isolated folly sitting in the middle of an expanse of featureless lawn . Rather than go that route of trying to recreate a stately home in your 3 bed semi, perhaps consider where you spend your time, is it the little seating arragement in the corner of your patio or is it to one side where the sun is always present late into the summer evenings. It may even be the small area in front of your french doors from where you can see the children and keep an eye on the dinner, listen for the door bell or keep one eye on your favourite soap opera.
My point is really to choose a fountain to meet your needs rather than the formal asthetics of some garden designer who will never spend more than a few hours in your garden, a garden fountain or water feature should enhance your life, not just visually as an ornament but also in the sounds of running water and the twinkle of reflected light that comes from being close to water. So a small garden fountain close to your house may well be more effective than a larger one 30m away.
Also consider what you will be doing when around your fountain or water feature, if you will be sitting, perhaps listening to the radio or reading your favourite magazines, so you may be dwarfed by the 6ft high 4 tier fountain that looked so good in the picture or the vast expanse of the garden centre display area
One guidline to consider is that the larger/higher your fountain the further away it has to go from your seating area, the smaller the fountain or water feature the closer and more intimate its location, any thing above 1.5m is likley to overpower anything else around it for at least a 2m distance. If you want to drown out traffic noise a small garden fountain close to your seating area may work better than a large one which is further away, idealy place the fountain between you and the noise but as close to you as possible.
On hot summer days a fountain will cool the air around itself, if you have a prevailing direction for breezes in your garden try and position the fountain upwind of your seating or patio, this way you will benefit from its cooling affect.
Positioning a water fountain close to a window can in hot summer weather introduce a cooling breeze into your house
This depends on who your asking, if your asking a retailer who is selling stone or plastic garden fountains you will undoubtably get the answer that stone or plastic is best and the same can be said for manufacturers using any other material, the truth is each material has its good points and bad points so here are a few
Stone garden fountains and water features - is the traditional material used for decorative fountains, most produced today are made from concrete which is poured into a mould to produce a dense stone casting that is cold to the touch, hardwearing and as close to natural stone as you can get without carving from a single block. usually supplied in sections as they tend to be heavy. Limestone or some other agregate together with sand cements and pigments will be used in thier manufacture, most 'marble fountains' are mainly imported from italy or spain and manufactured by adding marble chippings to white cement to produce an imitation marble. Stone fountains produce a crisp clear water sound as opposed to some other materials such as plastics which tend to damp out the sound, imagine running a tap into a plastic bucket and you can realise the difference in sound quality. If left full of water in freezing conditions stone fountains and water features can become cracked or fracture in the same way that natural stone will, so a little maintenance prior to the winter setting in is required such as draining the fountain or water feature, this is not usually a problem as no matter which type of fountain is bought the pumps will require a clean out at least once a year.
Painted stone fountains - are perhaps a thing to avoid as the paint obscures fine detail of the castings and can hide a multitude of problems such as repairs to poor castings that will crack with the first frost. Painted stone fountains also peel exposing the basic cement colour underneath, these painted fountains are very often of poor quality and should be avoided. Better to look for stone or concrete fountains with pigments or sands added to give the final colour, you can see the raw casting surface and so by necessity are usually of a higher quality than the painted ones.
Plastic garden fountains and water features - are generally cheaper as they are mass produced usually in the far east and imported in bulk. There is a huge range of plastic fountains avaliable, sometimes under strange material names to confuse the buyer, these types of garden fountains and water features are usually hollow lightweight constructions which is good for easy handling and shipping but not so good on a windy day. Plastic fountains are low maintenance but will never age well, the paint will fade and peel and the plastic will go brittle with age. The all important sound quality may also be low as the plastic hollow construction absorbs the sound of the water. Unlike stone fountains that are cold to the touch plastic fountains are warm to the touch, this leads to greater evaporation so more frequent topping up may be required. Plastic garden fountains and water features are cheap and if thats your only criteria then thats probably all your interested in
Glass and mirror water features - mostley avaliable in geometric shapes they tend to be simelar to the plastic options avaliable mirror surfaces are usually plastic stuck onto hollow plastic castings, there are some quality products out there but look closely before buying to tell if its a quality product or cheap import
Next....Buying a fountain or water feature online
Portland (P)
A soft natural white colour stone
Bath Stone (BS)
A light honey colour stone
Green (G)
A medium olive green stone
Terracotta (T)
A pale and sun baked terracotta
Dark Terracotta (DTC)
An earthy Tuscan red/brown terracotta
Slate Grey (SG)
A cool dark slate grey
Colours may vary slightly due to digital processing