A different approach to HTML templating

For comparison: profile.erb

<h1><%= _('Profile') %></h1>
<%= form_for @profile, :url => user_profile_path(@profile), :html => {:class => 'profile'} do |f| %>
  <%= render 'shared/errors', :model => @profile %>
  <dl>
    <dt><%= f.label :name, _('Name') %></dt>
    <dd><%= f.text_field :name %></dt>
  </dl>
  <dl>
    <dt><%= f.label :email, _('Email') %></dt>
    <dd><%= f.text_field :email %></dt>
  </dl>
  <dl>
    <dt><%= f.label :gender, _('Gender') %></dt>
    <dd><%= f.select :gender, Profile::GENDERS %></dd>
  </dl>
  <fieldset class="services">
    <% Profile::SERVICE_TYPES.each do |type| %>
      <% f.fields_for :services do |ff| %>
        <% ff.fields_for type, @profile.services.detect {|s| s.service_type == type } || @profile.services.build(:service_type => type) do |fff| %>
          <dl id="<%= type %>_field">
            <%= fff.hidden_field :id if fff.object.id %>
            <%= fff.hidden_field :service_type %>
            <dt><%= fff.label :url, _(type.titleize) %></dt>
            <dd><%= fff.text_field :url %></dd>
          </dl>
        <% end %>
      <% end %>
    <% end %>
  </fieldset>
  <dl>
    <dt><%= _('Options') %></dt>
    <dd><%= f.check_box :public %><%= f.label :public, _('Show public profile') %></dd>
    <dd><%= f.check_box :newsletter %><%= f.label :newsletter, _('Receive updates via email') %></dd>
    <% if @profile.admin? %>
      <dd><%= f.check_box :show_admin_status %><%= f.label :show_admin_status, _('Show admin status on profile') %></dd>
    <% end %>
  </dl>
  <%= link_to _('Cancel'), user_profile_path(@profile) %>
  <%= f.submit _('Save') %>
<% end %>

For comparison: profile.haml

%h1= _('Profile')
= form_for @profile, :url => user_profile_path(@profile), :html => {:class => 'profile'} do |f|
  = render 'shared/errors', :model => @profile
  %dl
    %dt= f.label :name, _('Name')
    %dd= f.text_field :name
  %dl
    %dt= f.label :email, _('Email')
    %dd= f.text_field :email
  %dl
    %dt= f.label :gender, _('Gender')
    %dd= f.select :gender, Profile::GENDERS
  %fieldset.services
    - Profile::SERVICE_TYPES.each do |type|
      - f.fields_for :services do |ff|
        - ff.fields_for type, @profile.services.detect {|s| s.service_type == type } || @profile.services.build(:service_type => type) do |fff|
          %dl{:id => "#{type}_field"}
            = fff.hidden_field :id if fff.object.id
            = fff.hidden_field :service_type
            %dt= fff.label :url, _(type.titleize)
            %dd= fff.text_field :url
  %dl
    %dt= _('Options')
    %dd
      = f.check_box :public
      = f.label :public, _('Show public profile')
    %dd
      = f.check_box :newsletter
      = f.label :newsletter, _('Receive updates via email')
    - if @profile.admin?
      %dd
        = f.check_box :show_admin_status
        = f.label :show_admin_status, _('Show admin status on profile')
  = link_to _('Cancel'), user_profile_path(@profile)
  = f.submit _('Save')

profile.html

<h1 x-loc>Profile</h1>
<form class="profile" x-action="/user/profiles/{profile}" x-method-for="profile">
  <div x-partial="shared/errors" x-yield="profile->model"/>
  <dl>
    <dt><label x-for x-loc>Name</label></dt>
    <dd><input type="text" x-bind="profile.name"/></dt>
  </dl>
  <dl>
    <dt><label x-for x-loc>Email</label></dt>
    <dd><input type="text" x-bind="profile.email"/></dt>
  </dl>
  <dl>
    <dt><label x-for x-loc>Gender</label></dt>
    <dd><select x-bind="profile.gender" x-options="global.profile.genders"/></dd>
  </dl>
  <fieldset class="services" x-each="global.profile.service_types->type">
    <dl x-id="{type}_field">
      <input type="hidden" x-bind="profile.services[service_type=type].id" x-if-exists/>
      <input type="hidden" x-bind="profile.services[service_type=type].service_type"/>
      <dt><label x-for x-content="type.titleize" x-loc/></dt>
      <dd><input type="text" x-bind="profile.services[service_type=type].url"/></dd>
    </dl>
  </fieldset>
  <dl>
    <dt x-loc>Options</dt>
    <dd><input type="checkbox" x-bind="profile.public" x-boolean/><label x-for x-loc>Show public profile</label></dd>
    <dd><input type="checkbox" x-bind="profile.newsletter" x-boolean/><label x-for x-loc>Receive updates via email</label></dd>
    <dd x-if="profile.admin?"><input type="checkbox" x-bind="profile.show_admin_status" x-boolean/><label x-for x-loc>Show admin status on profile</label></dd>
  </dl>
  <a x-href="/user/profiles/{profile}" x-loc>Cancel</a>
  <input type="submit" x-loc>Save</input>
</form>

I think, for me, it's difficult to have an opinion that is well informed enough without using it for a while in various situations. Also, there are some designers who love to work in the actual application codebase, enjoy a terse language like Slim, and can even be taught enough Ruby avoid being stalled when they need a data structure or helper method. Then there is the fact that some template languages work good in one place and not in another. Sorry I can't give you a more hot/cold response :)