I had a Graco safe seat for my daughter up till 13 months, then switched to the Britax Decathlon. She's tall (93%) and thin (15%), so I picked this particular brand because in online comments/reviews they seem to handle tall kids better.
I'm sure your seat is fine, and the Britax is a great brand. We decided to do the Britax in the "family car" and a less expensive but reliable brand in my husband's car (he does daycare pickups 3 blocks away and some grocery runs, nothing extensive).
Perhaps you can use the Evenflo in the 2nd car (if there is one), and get a Britax for the 1st car.
You should also check out http://www.car-seat.org, and search for similar threads of conversation (particular to your brand) and you can even post a question. I found the site extremely helpful when researching our 2nd car seat. The people online are all experts, and their advice was excellent.
Good luck!!