Renfe VS Loco2

Both sites originate in a country with different currency so their conversion might be different, or they might have a booking fee of differing costs.

I bought mine from Renfe, but not all North Americans have success this way. A tip, first set up an account on Renfe, so if you do buy there, you can check your reservations without having to rely on an email trail. There is an app, but I wouldn't recommend it for limited use and you can maneuver the full site better. If I would have had problems, then I would have used Loco2 for ease.
Many don't find Renfe very useful or user friendly, but I was okay with it. It did take a bit for me to realize that levels of seats vary and they are not all set at say - discounted fares; so you need to look at all drop down menus to choose. I occasionally found a higher level of comfort cheaper than the cheap seats, or only a few dollars more so worth it.

I totally get the worry about buying too early. I guess you can get around it by comparing some costs by making a dummy booking for a few days from now (to get a base price on walk up tickets) vs tickets with full or partial change fees or refundable. ...but you need to know the rules of whether you can use the ticket if a 'no show'.

The alternative is a fully exchangable ticket a little later than desired, and try to change for an earlier train if you arrive ahead of time.

Just for background: RENFE is "the" train operator in Spain (thus "the horse's mouth"!), all the other webs also selling tickets (Loco2, etc) are middlemen.

I purchased tickets on Loco2 for a trip coming up in 2 weeks. I had heard the Renfe site was difficult so I went right to Loco which was very user friendly. The actual tickets are the same price on both. There may be a slight service fee on Loco but it was worth it! Many weeks after I bought my tickets I realized I put in the wrong date. I panicked and emailed Loco2. They immediately emailed me back and changed the tickets. I was amazed at what great customer service they have. I would definitely recommend them for ease and service.

I also used the Loco 2 site, just because I found the Renfe site really hard to use. If there was a price difference, it was minimal and (in my opinion) worth the ease of the website. Also, I just emailed Loco2 today to ask for a change in one of the tickets (to leave out of the Antequera-Cuidad station, rather than the Santa Ana station), and they emailed back within a couple of hours with new tickets. Super helpful.

I do agree with you guys, RENFE is notorious for its awful website and its worst customer service!

It ain't that bad...when my Rodalies train is delayed for 15 min they totally refund my ticket! I have never seen that on the other commuter transport networks in Barcelona neither in Europe, at least 30 min for a partial refund!