I've got a bit of a soft spot for sunglasses myself, and have had this conversation many times over.
Avoid polarised - For VFR flying the polarisation stops the glint and glare from anything horizontally polarising light. This includes water (from lakes and rivers which might otherwise be very useful for navigation), some runway lighting, and other aircraft (useful to see them so you don't hit them).
Some argue that polarising also affects visibility of 'glass' instrument panels and also visibility through some windshields which are polarised also. Having never flown with polarised glasses and glass cockpit at the same time I couldn't comment either way, but best to check if possible before you buy if you do get polarised.
Thin frames - If you wear an 'over the head' headset then you'll want something with thin frames. Very thin frames. Ray Bans aviators, Serengeti, and Oakley wire frames all work. The more sporty types of Oakleys are't suitable at all, but the brands you mentioned don't seem to style anything like those anyway.
Try them on! - You'll be wearing them a lot. Don't get something that looks amazing but isn't comfortable after half an hour under the headset.
Good coverage lenses - This doesn't always mean aviator style glasses, but you do want a pair which have a good coverage over the likely places you'll be looking. You won't want a thin lair of lenses which let glare through around them when you pop out of cloud. try them on and move your head around all over the place whilst looking at one point - Do the lenses change colour or tint, or are there any large uncovered areas?
Neutral coloured lenses - Try to find a lens with neutral coloured lens. Anything with a grey base is a good bet. The reason for this is that you will want good colour perception. Whilst the fancy coloured lenses look good, if they are a red/blue/green base then colours will become distorted, probably not best for the runway lights when landing into a sunset eh? This isn't to say you can't have a fancy lens colour, just check the lens base colour first!
Avoid Transistions lenses - They don't work for aviation! Some windshields are polarised and UV blocking, which stops the transitions from... well... transitioninging
This means you could be flying in brilliant sunshine, with no tint at all. If they do work in your aircraft, then they will not be able to keep with the changing light (think how often you look down at the fuel guage, or the map/plog/AI etc). They are really not recommended, and I would avoid them completely.
Hope this helps,
4015