As you may have heard, things are starting to look a little different across many Google products—and today, Blogger is the next product to get a makeover.
Right now, it's easy to try the new GUI - and if you don't like it, it's also easy to return to the old GUI. Like all Blogger upgrades, don't plan on it being an option, for very long.
Try the New GUI. If you decide that you don't like it, let Blogger know. Every New GUI display has a gear icon in the upper right corner, or a direct link to "Send feedback" in the lower right corner. The "Send feedback" wizard makes it pretty easy to identify any features, on any specific display, that you think can be improved.
As with every Blogger feature, nobody will be well served with Blogger having to maintain redundant versions of their product, for an extended amount of time. The Classic GUI may be your preferred version of Blogger - but it's not going to be around, forever.
Try the New GUI - now, and let Blogger know what you don't like - now. Give Blogger feedback, so they can improve it, while it's optional. You may regret your immobility, later.