This brief set of paragraphs is intended to help you to choose the fly rod.
Most fly-fishers require their fly rods to fulfil different functions (in terms of species and size of fish and prevailing conditions). Consequently, fly rods may be selected with compromise (versatility) of criteria. A fly rod fulfilling several requirements may be a better purchase than one with more-tightly defined function. This versatility is often reflected in length, fly line weight, and 'action'.
The optimum fly rod length varies according to its function but it also varies by individual and even by country (for example: UK salmon anglers often favour long rods of 15 - 16 feet whereas their American counterparts favour much shorter 9 - 10 feet rods). A long rod does not necessarily assist casting but it may help line control in the water ('mending' is a good example). A longer rod may provide better leverage when playing large fish too.
Clearly, dry-fly fishing for small trout will require a different rod to that used for large pike or salmon - so it is likely that many fly-fishers will acquire several different rods.
Fly Line weight:
The weight of fly line is hugely important (regardless of whether it floats or sinks). To present a large lure, at considerable distance, will require a different line weight to one used for tiny dry-flies at close-range. The line weight should (ideally) match the (AFTMA) rating of the rod but even here, there is a little room for compromise - as some anglers 'aerialise' more line than those who 'shoot' line through the rings .... and this may mean that they find casting easier with a lighter line-weight than an AFTMA match. AFTMA grades line by the weight of the front portion rising from 1,2 3 (light-weights) to 10, 11,and 13 eight lines (which are heavy and are intended to 'load' big/heavy rods).
This term indicates where the greatest flexing occurs within the curve of a fly rod. Some fly rods bend mostly at the top end (tip-actioned) while some bend throughout their whole length - different fly rods suit different functions and the fisher's casting style(s). The selection of the rod's action is a very individual matter. As a rough guide, 'through-actioned' rods tend to accommodate variations of casting style whereas 'tip-actioned' rods tend to require crisper timing to achieve best performance. The thickness of the rod blank will determine, to some degree, how it cuts through the air while casting. The ability for the 'blank' to return to its original straight election is determined by its elasticity (do you remember your school-day physics lectures about Wright's Modulus of Elasticity ? !!). The best blanks do this rapidly with modern, fine (lightweight) carbon fibre materials.
Number of Sections:
The number of pieces a fly rod breaks down into is an important specification. A fly rod with few joints will have a smooth bend whereas one with several joints may suffer somewhat from the bend being interrupted by the joining sections (although most modern fly rods are particularly good in their joint design and do not suffer much from this phenomenon). To store, or for ease when travelling, multi-sectioned rods are deservedly popular, although two, three and four-piece rods still retain conventional popularity.
Many fly-fishers have quite fixed views about the type of line guides (rings) which suit them best. Some like 'snake guides' where fine (light) wore is used to hold the line close to the rod. Other prefer stand-off and 'lined' rings with single or two-leg attachment. The snake guides seem to be most popular presently (probably because they are in concert with the modern quest towards lightness).
Handle shape, and Colour/cosmetics:
These elements are really 'in-the-eye-of-the-beholder' ..... in other words they are personal choices. Some anglers prefer matt finish to the rod blank (to minimise flash.) There is a huge variety of line-guide tying colour to choose from, and when these elements are coupled to the specs described above and the profile of handle and all the other specifications ..... it makes for a difficult choice !!
Perhaps the most obvious specification is cost ...... buy what suits your pocket ! A very expensive fly rod will not make a wonderful caster out of a novice (although he/she may enjoy owning a really fine fly rod). It may be a more sensible option to buy more than one rod within a sensible budget rather than buy a single expensive one.
Most of the time, you get what you pay for ..... but keep in mind that a fly rod is just a bendy stick !!