I use a Sworovski scope woth an 20-60 zoom, using the 20X to locate the aircraft as this will give the widest and brightest view, once located you can then zoom in, however you will need a tripod as hand holding will not be possible. It's hard to recommend one piece of equipment as it depands on many factors not least available funds, you get what you pay for. Look out for used examples you can get good value this way and you can try digi-scoping too.