as someone who has watched every guard game ever, i can safely say that it is tex. ofc, i am considering Saya's entire stint with them and not just Stage 1.
The problem with Saya is that once Jett was nerfed, he caused problems for The Guard because his agent pool was not very good. He either had to play Chamber (which unlike most teams, The Guard shouldn't have had him on Chamber), or he had to play Jett. He wasn't good at Raze or Neon (AT THE TIME), so they struggled to adapt to the meta, which was evident in Stage 2 and LCQ (they were playing jett on fracture ffs). Ofc, if current Saya rejoined the core, it would be a vastly different story. He's really good at both Raze and Neon now, so he would fit seamlessly.
tex on the other hand, never had any issues with his agent pool on his Guard stint. They never had to build around him, and he did his job very well. We can see the stark contrast between tex and leaf rn because G2 is struggling MASSIVELY with first engagements. tex was extremely reliable at getting the first blood, especially at Ascension, but leaf is having a hard time replicating that success (not entirely sure if thats his fault or the team's fault). tex was a very reliable player towards the end of his stint and he really started to take over games as well.
leaf just needs more time and he can definitely be the best of the 3, I won't say much about him until VCT starts.
the best fit for G2 rn would be keznit or aspas (barring language barriers). If language barriers are something to consider, then getting Saya back or Victor/Jawg would be best for them. zekken would also be good.