I like riding with other people which is why I organise so many forum rides round these parts.
I agree with Globalti that it is good to ride with people who like to go at your speed, the trouble is - at the moment, I don't even ride at my
own preferred speed! My fitness is so far below what it used to be that everybody has to wait for me at the top of the hills and there are always plenty of them on my rides.
As the years go by, I'm finding it harder and harder to motivate myself to go out alone. The sun is shining today and I intend to go for a ride but I've been putting it off for over an hour and still don't feel that keen. The stupid thing is - I know that within 10 minutes of setting off, I'll start enjoying the ride. Having a riding partner is a great encouragement to get those first 10 minutes in!
Having said that, I've done many rides over 100 miles solo and those have been fine. I never attempt a ride that long unless I really feel 'up for it'.
It's the shorter local rides that I've done hundreds of times before over the past 20 years that can be boring without company. If I was really fit, I'd just ride very quickly and get them over with but I'm too slow. I'm averaging 10 mph on the hills where I used to manage 16 or 17!
So, I'd suggest a bit of both - do some of your rides solo, and make an effort to find riding partners for the others. If you don't fancy joining your local CTC or road club, just start a thread here on CC asking if anybody fancies a forum ride in your area (
example). You should be able to find at least 4 or 5 people who are interested. I did that up here when my former cycling buddy emigrated and I've ridden with about 40 CycleChatters since then, about 10 of whom are now regulars.
Make it clear that yours is a social ride and that nobody will get left behind but state how long the route is and give an estimate of what speed you are likely to ride at - it is best not to get a complete novice turning up to do a 50 mile ride when they get tired doing 5 miles, and you don't want people who expect a 25 mph chain gang ride!
Work out an interesting route with a good cafe or pub stop about 2/3 of the way round. Take photos on the ride, and post some on your ride thread afterwards with a write-up of how things went. You'll get people coming on the thread saying how they wished that they had been on the ride, and asking when you are doing your next one!