I can't tell you what choice make, but you're eventually going to need to get your ATP. There aren't many charter outfits thay will hire a SIC with just a commercial. Although the regs say you only need a commercial, the company's insurance will probably dictate you have an ATP. Some companies will have you do an ATP checkride as part of their training, so you may not need an actual certificate but you will have to meet the minimums to earn an ATP.
I would advise having your certificate as that would be one less thing for the company to descriminate against when they are comparing you to other candidates. Also, if you don't have a college degree, get one. Same thing applies. If all the other candidates have degrees and you don't, guess who won't get the job. Don't make make it easy for Human Resources to say "no".