Some of the others beat me to giving a reply to the question, but I think there's still more I can add in regards to the role mechs or frames can play. I've said it before, but it seems like it was missed; when ships and fighter-bombers aren't there for you, things like these become a godsend because they stay with the infantry like a loyal dog. After all, the enemy may do something horribly right on their part while playing for keeps. In Star Trek, this reality became pretty painful whenever ships couldn't give Star Fleet personnel support, leaving them exposed and with nothing.
As for what the SAoY could choose?
I would not recommend going for a walker design Wes, primarily so that players have something more relatable and also playable should a GM wish to make a plot or players use them. In most other instances, they'd still take a backseat to PA though. Another consideration is that a humanoid design is more flexible in that it has better melee options if it came down to it. Such a design is simply more autonomous. In comparison, a tank is a lot more vulnerable close-in despite having similar firepower and can't be as 'resourceful' as a frame. If you'd prefer a design that's about 3 meters in height similar to Fred's Akuma and the ED-209, you may want to take into consideration the Armored Shrikes from Blue Gender to get an idea of their scale, though probably not asthetics or even performance. It's not a new anime, but for our purposes, it's worth taking a look at, as the pilots have an open cockpit which further helps give us a good idea of just how big or small they are.
A three meter design like that is compact, easy to transport and nimble, however, there's a good chance it'll be in the same ballpark as a decent tank in terms of firepower at best. Not only that, but that size category looks like it's already taken up by the TASHA. You may be better off with a 6 Meter design, which would be able to house a lot more firepower, and act as a peer against things like the NMX Ravager. To get a sense of scale - but again, not performance or asthetics - the Titans are a good bet. The best thing about them is that they're roughly the size of several other frames in SARP as well.