In terms of the main page, out of the box Alloy has about seven different layout options, some are pretty standard but some are really nice, and make the main page feel a lot less like a blog page but a regular content page.
Posters main page is a little less flexible in terms of layouts; as you mostly have stacked items or a grid layout.
In terms of spacing elements in each post on the main page, Alloy has a lot of options in settings: Margins, borders, shadows, and so on. What it lacks in the settings options you can handle with custom CSS.
Poster though gives you complete free-reign of the layout for each blog item on the main page. You can go with the standard image above, then header, then meta, then description etc. Or something else entirely. You design the main page item layouts yourself using a template.
This is a major boost for Poster as you get ultimate layout control. But, with that control comes the requirement that you learn to use templates, which is easy enough once you get your head around it, but can be a learning curve for those used to drag and drop and settings etc.
Once you open an item to view the main article/blog, Alloy is pretty standard but again does have some nice design and layout controls built into the settings. Poster once again gives you complete control here, as again you first build a template to layout the content as you want. So Poster: More control. Alloy: Easier deployment.
The big difference comes with the blog/article content though. With Poster anything goes. Almost all stacks will work inside a Poster item. Whereas with Alloy, the editor interface that allows you to actually create your blog posts isn’t inside RW but in the browser and creates a Markdown file, so you are a bit restricted as to what you can do. So it’s headers, text, images, video etc. which really is pretty much all you normally need in a blog post. But, sometimes it’s nice to be able to add more complex stuff, a la Poster and using stacks.
Bear in mind that if using Poster with a Markdown folder, the same restrictions apply as per Alloy (both use Markdown).
I realise this is most likely little help still, but really unless you said “I want to be able to add blog posts today via the browser”, in which case you’d have to go Alloy, there is very little between then, in terms of the end result. The big differences are how to arrive there: Poster is all inside RW, Alloy is all inside the browser, once it’s set up inside RW.
Poster: Small business website design and marketing news.
Alloy: Latest news and articles about bulk email makreting.
Poster: News from Template Repo.
Alloy: Wedding venue and events news Bangor | Field Of Dreams NI
I could go on. I’ve loads!