I just came across this discussion, interesting as I have belonged to both groups. I still have a website on broadjam, but gave up my Taxi membership a couple of years ago as it was costing about $350 a year. I pay $35 to $50 to keep my 50 songs and website on Broadjam. I had been with Taxi for over 10 years with an occasional year off when money was tight or I had someone else to pitch my songs. I've had numerous forwards with Taxi, had one song published and sold one to an independent movie, which unfortunately was not a big hit. I know several of the Taxi screeners or ones who used to screen for them and had my song "Freefall" on the Taxi promo CD "Country Jams" which included "Buy Me a Rose" and songs by Randy Bachman, Jimmy Muffin, Larry Cordle, and Lindy Robbins. Taxi pitched these songs on Music Row and I got to meet Rex Benson who published that song, almost got it cut and published my song " The Other Side of Goodbye" which he pitched to some major acts in Nashville. Rex no longer works for Taxi as he needed more time for his own Publishing business. I've been to several 'Road Rallys" and I've seen Broadjam there, I'm forgetting the gentlemans name who runs it.
The biggest difference is with Taxi you always get a professional opinion of your song and it's going to be much better to help you meet the bar and to try to fit you into a slot or style that can be sold. Also you'll get the chance to network more, especially at the "Road Rally" you can make some good contacts. Of course as usual a lot of it is up to you and I was lucky at the time to be living in LA where I could go to work shops with industry professionals on a regular basis. Taxi still lists songs for Country and other genres and they have a "dispatch" service which is for TV and Film mostly. This costs extra.
Broadjam was used by Taxi as their way of delivering songs online, before you had to mail in cassettes and Broadjam was much better, faster and easier. They have Top Ten lists and categories kind of like Soundclick and lots of contests. A friend of mine has been a top finisher in their Six Pack Songwriting contest with lots of nice prizes. Just like on Taxi you find people at all levels of talent and success there. Because it's a peer review system it helps to be a self-promoter there especially and the blogs seem be important. I've had a whole bunch of #1 and Top 10 songs on Broadjam, but don't put my songs up for review currently. You can submit your songs for listing for TV and film there too. It can be fun and you have a more direct connection to other artists than at Taxi where you are trying to impress the screeners. And there are industry professionals who are around looking for songs and talent. You get a site on Broadjam where you can list info about yourself and your gigs, so good for a self promoter.

Pete