Just my two cents worth.
I did my initial twin on a seneca as part of building hours for my C.P.L.
Subsequently, my first charter after gaining my C.P.L. with that organisation was in the seneca, and I also did a couple of ferry flights for them also.
Did it have a great impact on my flying career progression? Probably not, but then again, it didn't hurt either.
If you can afford a twin endorsement, go for it.
It is still a buzz that I clearly remember today landing an aircraft with a fully-feathered engine.
Good luck whichever way you choose to go!
Also, why make things harder for yourself? if you fly a twin in your CPL command time building, the testing officer may require you to fly the most complicated a/c you are endorsed to fly, and why bother yourself with engine outs and assymetric handling in a CPL flight test when you can fly in a single, get a job and start building hours!
I was told this sort of story when I did mine, but don't believe it. I completed my C.P.L. in a Piper-Arrow. The testing officer cannot put you at a disadvantage by requiring you to do your test in a twin. The only requirement from memory is that your test must be conducted in an aircraft with a Constant Speed Propeller.