Hi,
You always want your page to load as fast as possible, there are several ways to achieve this in relation to your buttons.
– Make sure your images are optimized so the file size is as small as possible. There are several tools online that can help you do this (not sure of them offhand). You can also use programs like photoshop / image ready and paint shop pro to reduce file size.
– When creating your pages, make sure that the image size and width are included in the IMAGE tag, that way your page text will load even if the graphics haven’t loaded.
– In general text links are said to be better as you can have anchor text (desired keywords) link to the page which is said to help search engine optimization.
Hope this helps!