The smaller the engine, the better.
Parents as named drivers also bring the price down too
Black boxes make it cheaper too, but I really wouldn't go for one of them
i got a shitty little R reg fiesta as my first car, my insurance was £700. Getting my no claims up on my first couple of cars brought my insurance down to below £300 until I crashed last year and now my insurance is around £500, because my dad opted to up his insurance premiums whilst keeping his no claims so mine stayed at a lower price, but yeah, basically go for what's affordable until you get enough experience to bring prices down.
even new fiestas have 1 litre engines that have fairly low insurance costs in the scheme of things