First consider the price. There are free form creators, but in my experience they're worth what you pay for them. They're typically exceedingly limited, and will produce amateurish results. Some will give you a better product if you pay for a premium version, at a price much higher than FormMail's. Others are too hard to work with. FormMail is nearly free — per month only a dollar per form! (FormMail has in the past offered a completely free version, with advertising, and you may see a reference to the free version on its website.)
I frankly don't know how FormMail provides what it does for the tiny amount it charges. It seems that the owner, Roger, treats it as a hobby rather than a business. The various options should meet any needs. Documentation is extensive. You don't really need to know HTML, although a basic knowledge is helpful. A huge plus is the level of support you get for your one dollar. With rare exceptions it'll take only a day or so to get any help you might need.
You don't have to pay even the tiny cost until you've successfully created your form and have decided you want to use it.
There are two downsides. First, you have to pay via PayPal, which I don't like. (See my PayPal review.) Second, you have to "subscribe" for 6 months at a time, with opt-out renewal. The 6 months are certainly fair, but I try to steer clear of any opt-out payments.
All in all, however, I strongly recommend FormMail if you need to create a professional-looking form.