Should I use Pre Get Posts or WP_Query

pre_get_posts will run the same query, so both will take same time. But, If you utilize pre_get_posts action you will save one or more SQL queries. Right now, WordPress is running default query and then you run your query with this function which replace the results of the default query (resulting, default query is of no use). Below is how you can move your $args to

function custom_pre_get_posts($query, $posttype="dealers", $poststatus="publish", $paidvalue="1", $taxtype="any_default_value", $geo='any_default_value', $brands="any_default_value") {

    // filter your request here.
    if($query->is_category) {

        $args = array(
            'post_type' => $posttype,
            'post_status' => array($poststatus),
            'orderby' => 'rand',
            'posts_per_page' => 30,
            'meta_query' => array(
                array(
                    'key' => 'wpcf-paid',
                    'value' => array($paidvalue),
                    'compare' => 'IN',
                )
            ),
            'tax_query' => array(
                'relation' => 'AND',
                array(
                    'taxonomy' => $taxtype,
                    'field' => 'slug',
                    'terms' => $geo
                ),
                array(
                    'taxonomy' => 'brands',
                    'field' => 'slug',
                    'terms' => $brands
                )
            )
        );
        $query->query_vars = $args;
    }
}
add_action('pre_get_posts', 'custom_pre_get_posts');