Hi slant,
vertical or horizontal to me makes no difference at this point of time.
it used to but not anymore...and when i say it used to, i went for the lower profile i could get, after mounting it on the gun (for easy turning as mentioned earlier) i dont think it makes tha much difference...at leat not when the gun you(i mean anyone,.not YOU ) are trying to turn behaves like a lorry
but as i have learned and experienced, (at least on euro guns), what you need to worry is to get a decent reel that will do its job PROPERLY.
points to look for (at least this is my criteria)
1. Sturdy design. (parts wont take off when the travelling spear 'pulls' the components) some peopl ehave the reel loosened, some dont. im one of those that dont (at the moment on my current reel)
2. Easy to operate brakes (the knob should be designed so that its easy to operate with the glove on. also the brake system should not be affected by the reel turning - at least this is how i want mine-. there are several designs , some reels loosen the brakes when the spear pulls on them (some call it a 'Feature' of the reel...i dont think so....) if you have an easy brake knob that is not affected by the turning of the reel, i think thats the best....
3. the turning of the reel is not super free but at leat some tension is in place, at leat enough to not make a 'bird nest' -yes...it happens sometimes- just enough to control the unspooling of the line..... even cheap models have this, some expensinve one dont....
4. to have guides to keep the line 'within' the reel housing, to prevent the spirals from getting tangled on the reel itself.
5. PRICE
i have seen reels that are bascally plastic spools :rcard that also cost a bomb,(at that price i could buy another gun) but they are nothing but a plastic spool that costs a lot....that price is not justified at all , just the name on it makes them expensive !!!