In general, registering your brand name in plain fonts, such as Arial font, would give you broader rights. This is so as it would give you rights over the words themselves rather than the logo in a particular stylisation. Most of the time, customers are more likely to remember your brand name more strongly compared to how the logo has been stylised. As such, it is usually more important to protect the brand name.
To apply for protection of your brand name in plain font, you can simply type your brand name in the text box in the first step of the online form.
However, if your stylised logo contains a graphic or icon that is separate from the brand name, for example, the Nike swoosh, you may wish to file for the logo that incorporates the graphic and brand name as a single trademark. This is a good option, especially if you are sure that your company will not change the logo anytime soon.
If you also intend to use the graphical element in your logo on its own in some of your marketing collaterals, registering the graphical element as a separate trademark will be a good idea as well.
To apply for protection of your stylised logo, you can simply upload your logo in the first step of the online form.