Recently The Frumps (NSFW), one of the webcomics I follow, asked how its readers used its RSS feed and if we preferred having a thumbnail or a full-sized cartoon. I started writing a reply to them then realised that I wasn't just explaining how I used their RSS feed, but how I follow websites in general.
I follow quite a few RSS feeds, originally I used Google Reader but when when that closed I decided that in future I would have control of my reading and not be placed at the mercy of a third party service that could vanish at any time. Eventually I decided to use a self hosted copy of Feed-on-Feeds as my RSS aggregator. I use it for following webcomics, news (e.g. newspaper sites), science blogs, some technology bloggers I enjoy, as well as social, political and environmental bloggers. Occasionally if RSS isn't an option I'll subscribe to email notifications for a really good blog, but never (so far) to a webcomic.
As they can be absorbed so quickly, single frame or 3-4 frame strip webcomics are the majority of my feeds, but only a small fraction of my reading time. I find that even when I like a webcomic I stumble across, if it doesn't have an RSS feed. I quickly stop following.
I group the feeds by topical categories, e.g. Science, Software development, Auckland news but most webcomics are in two categories Cartoon for those that include the full cartoon in the feed and "Cartoon hidden" for those that either don't or offer better value on-site (e.g. SMBC with the extra frame button).
Blogs, news items and tech articles nearly always only have an introductory paragraph in the feed and with modern browsers it is trivial to open the page in another tab. As this allows me to sort out the entries I want to read and dismiss the rest I prefer working this way.
With webcomics scrolling through small strips and dismissing them once read is fine and I do read this way quite often, but webcomics are primarily a visual art form and opening the comic on its own page to read it in context usually gives a better aesthetic experience and I find I enjoy it more. For larger strips this is also more convenient as it also avoids scrolling around to read the comic then scrolling back to dismiss it and forward to the next comic. I know that this seems trivial, but over time it starts to grate and I'm also aware that "free" aggregators on someone else's hosting may not have this problem but I'm determined to stay self hosted for my reading.
It is, of course, not just a question of subscribing to webcomics but also unsubscribing if I become bored with it. Looking at the webcomics I have followed in the past, I tend to be much harsher on the ones that supply the full image in the RSS feed than the ones I click through to read. As they are in my face in the reader I tend to need to deal with them when they appear to comfortably move on to the next webcomic in that category but when it's just a thumbnail I can decide if I want to read it now or leave it for later.
Thinking it through this means that in general I prefer a thumbnail to a full sized comic in my feed.
There's a third option of having no image at all. This is the usual mode for most of the blogs I follow and quite common for webcomics. When dealing with webcomics do I prefer a thumbnail to no image at all? This is a hard one that I've been thinking through while writing this. I don't think it makes a difference to my reading habits, but the reader is more visually appealing when I have them so I feel I have a very slight preference to having the thumbnails.