depends on your boat, and whether you have space below decks for the motor. the size of the motor will depend on weight of anchor/chain and desired haul speeds. IMHO if you can install it, the vertical is better as it helps to protect the vulnerable electrical bits from all that salty water. On the other hand, if you ever have to convert it back to manual, the horizontal windlass is much kinder on the back than a vertical.
I have a lofrans airon 1000w
Totally depends on what your boat is and what will fit, but for me, vertical, small compact, neat and keeps the leccy bits dry. Quick do a nice range at very reasonable prices, as do Lofrans. Have a look at www.quickitaly.com and www.lofrans.it I`m going for the 2000 watt, "Rider".