When it comes to ease-of-use for a new shopper: 39DollarGlasses has been the standard to beat for years.
The site doesn't overwhelm with options; they are the only retailer to let you "print;" the glasses you're looking at (so you can print, cut them out, and try on in front of a mirror), and they've kept up with the latest virtual try-on features that allow you to upload a photo.
They have kept a clean and simple look: enough information available at a click if there is something you do not understand; while at the same time refraining from bombarding you with too many options and too much complexity.
Public opinion of 39DollarGlasses tends to be very positive. The biggest downside has always been that their glasses start at $39 whereas other retailers often offer glasses for quite a bit less. However the included cheap lens is "polycarbonate" which is a big step up from their competitor's base offerings: so $39 isn't as poor a deal as it might seem at first glance. That combined with the ease-of-use makes 39Dollars worth a look for any first time buyer.
39DollarGlasses websiteAt the forefront of pushing "virtual try-on" features was EyeBuyDirect. Back when these try-on features were newfangled technology, EyeBuyDirect was one of the first to put together a solid feature and promote it heavily.
The site does suffer a little from information-overload though. It is quite possible that a new buyer will be overwhelmed. Information is available but you should be slow, deliberate, and cautious while checking all the lens options as there is so much info thrown at you that details are easy to miss.
They are one of the cheaper options, so if you are comfortable-enough when browsing and putting together your first purchase, you could save a little coin. They probably aren't the first place you'd send your non-tech-savvy grandmother to though.
EyeBuyDirect websiteCoastal really tries to simplify the lens options and to an extent it works.
Where it tends to fall short is everywhere else. There is a little too much information overload going on. In some areas if you click for help (like if you want to learn to read your prescription), it just piles that information within the order box making it tougher to navigate. Other times "help" is simply marketing disguised as help for example the videos.
They do keep their phone number visible at all times though and where they managed to keep things simple: it does work.
Coastal websiteZenni used to be simple. As they have made changes (most positive) their marketing and SEO departments have destroyed most of the simplicity.
For example when viewing a frame there are 14 clickable options. 9 of them are "leave a review" or "share on facebook/twitter/etc" or "add to favorites"-style things. There are 2 more actual clickable help options but it is not clear that they are clickable. The younger crowd can usually filter the "social" stuff out and find what's important; but many from the older crowd will struggle more than they should have to.
Zenni can not be blamed too much though. Cheap prescription glasses are a competitive market and since 2011 or so, Google ranks sites primarily on social-media-popularity now (even solid sites like Zenni need a lot of social action or Google will lower them).
Short version is that if you can filter out some of the nonsense: Zenni's site is actually fairly simple at it's core. Not quite as much help is readily available as the alternatives but it's sufficient for most.
Zenni Optical website<< These aren't the cheap glasses you're looking for *hand-wave* (take me back to other cheap glasses options)
Some data might be wrong on this site. Do not take it at face value. Do your own research to verify the claims here.