To all intents and purposes the FED 1 and Zorki 1 are the same camera. That said, there are small differences and if you want a practical "user" then go for the later models. The very early ones often (should) have matched lenses and you may have issues if you try a different lens. The FED 1g (the one with the large "soup bowl" release collar) has a locking shutter - handy for long exposures without a cable-release. The very late 1g models have rather thin film rails too though and you have to pay particular care in loading if the film is not to derail.
Unless you have a collecting reason to go for one or another, I'd say a late Zorki 1 is the best user. Supposedly the dual-engraved (latin and cyrillic) models are better made but I am not convinced. Late models of both Zorki and FED have a 5-speed shutter rather than the earlier 7-speed version but in reality it makes no difference. The 7-speed ones have 20-30-40-60, speeds which are so closely spaced that they really only add to confusion. The later models have 25-50 to replace those. Less fiddling over which to use!
As for bottom loading, it's not difficult. Practice with an old film that you can sacrifice. Do cut the leader and do it properly. Other methods are not as quick and can cause damage. Look in the LTM section for a sticky on how to load.
Whichever you get, enjoy!
