Artscroll is crisp, clear, and easy to follow, and the siddurs are well made with strong paper and a binding that can take years of use yet allows you to lay the siddur open flat on a table and keep your page. I davened from the Yitzchak Yair until several years ago when I switched to…
Siddur Tefillas Shai. It matches Artscroll’s crisp clearness, and uses a beautiful, unassuming font that’s my favorite I’ve seen. Unlike my argument here, I have completely come around to having vehi noam tucked right into the weekday maariv before aleinu. The binding is strong, but unfortunately it doesn’t lay flat so well, so I lose my page when gathering the tzitzis for Shema. Also, only the tiny 5″ size is seemingly still in print. I managed to get a larger version a year ago, and hopefully over time it will start to lie flat on the table or shtender. This is my favorite siddur at the moment. Other than not lying flat, my only quibble is that some of the text is very small, which is difficult to read in poor lighting.
Aliyos Eliyahu – I grab this siddur in shul when I don’t have my own on hand. It has large, readable text, and stretches letters rather than spacing to achieve column uniformity, similar to a sefer Torah, which is a fun touch. It uses a different, neat looking font for pesukim, which clearly identifies them. It also lies perfectly flat on the table or shtender. It follows the nusach of the Gra, so there are some differences from how I daven nusach Ashkenaz.
Tefillas Kol Peh – I have a pocket sized version. It has an old fashioned feel to it which is nice, and I like the font, though sometimes words run together with no spacing. Rightwriter mentioned how the font size changes from paragraph to paragraph, and this feature is really nice in some places such as enlarging the 4th brachos in each of the Shabbos tefillos, but on the downside there are a lot of important tefillos that get squeezed in with tiny, hard to read font sizes, even paragraphs of krias Shema. Also, while I understand space saving, I personally don’t like when mincha and maariv are squished together with the ashrei of mincha spread out over like 10 pages with 2 lines on each page, with maariv underneath. Others may prefer this.
For someone new to davening, I would recommend Artscroll’s “Kol Yaakov” English/Hebrew siddur. It’s a lot of page turning, but it includes a bunch of helpful instructions (where/how to bow, when to say amein or not, etc.) and it marks out the points in each paragraph where the shaliach tzibbur usually picks up. It also marks where the shva na’s are (so do the Yitzchak Yair, Tefillas Shai, and Aliyos Eliyahu).