The best exercise is something you enjoy and are likely to continue.
If you don't like it, you won't do it.
Some are motivated by competition, some by companionship, some by weight loss (or gain), some by mental relaxation, some by body image, ... consider what will motivate you to continue when choosing what to do. And remember, you don't have to restrict yourself to one exercise - I walk, run, cycle, spin, climb and lift weights plus try out a few other things when they take my fancy: I did some flying trapeze last year.
Edited to add: some exercise will raise your BG during the exercise but most will reduce it overall. Typical exercise which raises BG is resistance training (such as weight training) and exercise for short periods such as interval training. But we are all different so try a few things out and see what impact that have for you ... and whether you enjoy it.