I am looking to buy a new bike. I have cycled seriously for the lst 12 months on a Specialized hard rock mountain bike. I am 59yo and originally choose that bike because I liked the security of the fat tires and I was concerned that a road bike would be less safe for me. I am biking primarily on paved surfaces and have improved quite a bit. I huff and puff up the hills but do it. I am cycling 50 - 60 miles/week (average 17 mph on level ground and 8-10 on hills)and think that I would like to bike with some of the local cycling groups on road. I will keep the mountain bike for rail to trail type biking but think I need to upgrade to ride with groups.
My question specifically is should I buy a hybrid or a road bike? What features of each would be important? Any advice would be appreciated