it's never a good idea to take champs that are nukes to rank 5 first unless you really like the character, that's just my opinion. r4 shocker would still kill the opponent with one sp2. if i had to pick I'd say either future antman or sentinel, jack is good too. I'm taking prowler to rank 5 btw
Here's my thinking for these first rank 5s. Either rank the one you love or rank the one that is future proof. In the case of Tech that means someone that can counter neuroshock as it's the future of Mutants that Tech will need to counter.
For the one you love, that's up to you. For me, I'm with Scion above - Prowler to r5 would be sooo fun imo.
For future proof: the options are Maker or Ruby Thursday. I'd also argue Jack/Bastion as reverse control immune and counter the current Mutant heavy hitters. I'd also include Fantman as he's proven his utility (huge damage and power control) have stood up to the test of time.
For me, if I get a r5 tech gem, it's either Prowler for fun, or hold and see how Ruby Thursday is if I can get my hands on her when the titan rolls over (if she's in it).
I r5 bastion
Mega dmg
It's between Fantman and Bastion for me, but Warlock has been solid for a long time, so he's a good long-term option IMO. Probably doesn't help you much, but that's where my mind is