For two cents... I'm a huge Orion fan in almost every iteration (not you, ON-1M). If you're looking to upgrade to each Mech's 3050 standard though... yeah, no.
The Zeus went from beast to... well, more-beast in '50, improving in some subtle but useful ways while not taking on a lot of the negatives other designs sometimes were saddled with. The old PPC vs. AC-5 question got answered with a big boost to the PPC's range, the ER large is a great backup to it, the pulse lasers lose range but gain accuracy (nice against fast Clanners), there's just nowhere that this design didn't get better. A bit warm, yes, but not to the point that it's impossible to deal with. There's no downsides or negatives here to speak of.
And the poster child for those negatives is the Orion, which was made into a mess of a design. I'm a firm believer an XL engine is a worthwhile upgrade if it really helps your design do something useful it couldn't have done before. Well... the Orion gained that useful LBX gun, so that's good, and the extra LRM tubes aren't unwelcome, but then... what, a Narc beacon? Seriously, THAT'S the tonnage use? Ugh.
Now, if you're going beyond that, the Zeus has some later handy versions, but Marik wisely tried again on the Orion with the 2M, and... yeah, this is what the Orion wanted to be all along. Gauss and LRM are a good start, three pulse lasers in close are a good backup (I prefer six standard mediums, personally, on the tonnage), tough as all hell, etc.? Yes please. And what do you know? There's nowhere this isn't better than the 1M, and while we're at it there's no unusual tech- you could build this in 3050 just as easily as '60.
So... intro tech, it's a punt, both are great designs. If you're upgrading to 3050 variants, the Zeus is a clear winner. And if you're willing to go straight to a 3060 variant in '50, the Orion is a great choice.