Mechanicals- Shoot very good, no tuning issues (from my experiences) flew same as field points, blades did not open on last deer of season but still made the kill. Good for beginners or those with limited time. Safer around the fumbling hunter. A new product.

Fixed Blade - More tuning issues, the blade is always open, easy to cut yourself, easy to sharpen, if shot is not a pass through the blades still cut with every movement, looks scary, used for thousands of years around the world.

I think those are fair comparisons.
Try both but you may want to go with the mechanicals your first season just to get off to a quicker start. Either way I guarentee you'll try both. Good luck with your new addiction!

Edit: My vote is for Fixed Blade.