Choosing between letter of recommendation writers for grad school
I would recommend the strong letter of recommendation, if he/she is able to give specific facts about what you did, or comment on your motivation, interest, and relationship. You might want to also let him/her know what you have been up to recently, so the reader doesn't think "well he/she used to be interested in math, but I don't know if they still are".

The main issue with "average" letters is that they are probably things that apply to everyone, so it's not really a benefit.

You might also want to make sure to "diversify" if you can -- so you don't end up with two letters that look the same. So if your other letters are coming from the community college, you might still want one from your stronger school (as long as they can write you a good letter of recommendation)