I keep everything online in observation.org . It took me quite some time to enter old data (and Ecuador is still a mess as at the time I only noted down 'East slope or West slope' in my field guide), but once that's done, it's sooo convenient!
I would urge anyone, even those (or especially those) with a small list, to enter their observations in any online system that tried and proven (ebird, inaturalist, observation, igoterra) before listing gets out of hand and you realize (too late) you need something better than a spreadsheet, and you end up with a backlog of sightings that seem too much to import in any online system. Just start with it, now. (ofcourse, if you are confining yourself to e.g. one country or a small part of the World, the needs for an online listing system are quite a bit smaller, but still, it's handy).
Remember (for those who do not want to give up on their privacy) you can enter almost anything either anonymous or just hidden for all others. So you have the benefits of having your data in the cloud (wherever you go) and not sharing your info (people can ofcourse see what you saw, and where, in most online systems, but you can shield that info).
If you think about it as a lister (at least that's my take), you want:
1. a sound taxonomic system (so you can't just put a cross in each fieldguide as they vary in taxonomy);
2. an easy-to-use app to enter data when travelling / in the field; I use observation (Obsmapp android or IObs apple), but I heard good things about e.g. Igoterra and friends who use ebird are saying it's very handy, so just use either one of those.
3. if possible, other species than birds.
4. preferably exact GPS (*) data stored with each sighting. Again, the same apps mentioned before can do this.
(*) Reasons to store data with exact GPS, and this had been discussed on this forum:
- you can go back 20 years and know exactly where you saw a certain bird;
- you can share the info with your birding friends (I mean: how are you listing and finding birds? thanks to the data entries in e.g. ebird by others. So why wouldn't you share your data as well?)
- you're, in a way (depending on how much you enter and how consistent, but even random entries are often considered in some studies) helping science with verifiable data.
- to evaluate whether a geographic split of subspecies into species applies to your sightings.
- To enjoy automatic list updates and, in many cases, to enjoy automatic changes in species (e.g. the moment Inca Jay was split from Green Jay, a moderator changed all of my Green Jays in S-America into Inca Jays). This also greatly helps you to get used to new names (for new or existing species), as field guides get outdated pretty quickly.
ps: there are some reasons why I don't use ebird, and the most important one is the messy GPS data in most ebird entries, but there are some more:
- Ebird taxonomy < IOC imho;
- No other species than birds;
- hotspots = encouraging people to ditch the most valuable part of the data, i.e. exact GPS.
But if there wasn't a better system, I would probably happily use ebird. Ebird shines in the way it represents the data with maps etc. But then again, you can only have data on your maps if you have people using the system, so again, I encourage everyone to enter their data in any of the systems I mentioned above...!