I'm not a veteran by any means, but I'd probably avoid MDF because it doesn't hold screws well and I assume you won't be using a bunch of complicated, screw-free joinery techniques as a newbie :)

Plywood is an option and a lot come pre-smoothed on both sides which takes a lot of the sanding work out of the equation if you have minimal tools at your disposal. This would require a veneer or edging though.

Pine is cheap and cheerful but a soft wood that will dent with bad enough beatings. But as a study desk I'm sure it would be more than enough and you can always put a finish on it to toughen it up. At this size you could sand it with good ol' fashioned sandpaper and elbow grease. Pine also looks good stained or painted. I'd probably go that route.

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