So apparently yesterday was my 7-year Subeta anniversary. Which I only found out today because I went to my user dashboard to go change a couple things. Way to pay attention, self. But now I'm giddy because OMGLOYALTYBOX and WTFDOIDOWITHIT?! I don't know what I waaaaant. So I'm doing what I do every year and asking you guys. Because I can't make decisions without asking the crowd I guess. [/failface]
[edit] Okay, let's break this down, shall we?
Option - 3 months of GA. I have a decent job so I can easily buy myself a GA every month now, but still, this would be nice to not have to pay. Although I only really use it for the extra wardrobe layer and the autopricing.
Option - Pet Slot. I'd love to have another pet, sure! But I don't have an idea for one, really. And if I got another, that would be 29 pets. I require an even number, lol.
Option - Change Pet Color. Do I want to change any of my pets' colors? I don't think so, but maybe.
Option - Stats. This might be a good option. My battle pet, Felinah, could definitely use an upgrade, but she's not really suuuuper high level or anything, so would it be worth it?
Options ,6,7 - Petname, Username, and Treasure chest. I'm not really interested in any of those at all.
I've mostly used mine for pet slots. I think I did color once. I'm keeping one as back up, and I just used one for 3 months of GA.
I get stats every time. I think my anniversary was yestersay or the day before but I don't want to boost my level up right now, so I'm avoiding user dashboard x)
I don't want it in my inventory xD But yes, battling is pretty much all I do here :p
I would say pet slot, because you are getting closer to being maxed out with the buyable pet slots and the loyalty pet slots go above the limit + you don't need to fill it up straight away if you want to stay on an even number.
I feel like pet slot is the only one really worth it because you can buy all the other rewards with money but the pet slot has the advantage of going above the limit of buyable pet slots.

Pet Slot. Everything else can always be bought with sP, at some point however you can only get another pet with the LB.
I would say pet slot, but oh god, 29 is a number from my nightmares. If I were going to be subjected to that number, I'd be tempted to forgo the pet slot unless I was sure I'd be able to buy another soon after (jk I'd get the pet slot anyway but just not create a pet until I found a name that really struck my fancy). But I'd still suggest the pet slot above the others by far, as you can always save it for when you do find a pet you really want and pets can be arranged so that that hideous number doesn't cause so much distress. shudders
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I tend to get stats. Yes, you could technically just do Shinwa's quests or buy her buffs-- but it's a quick and easy way. With GA I wouldn't, since-- you can use sp to buy it as well. Pet slots are the other option i'd choose if I had an idea of what pet I wanted to get.
I recommend a pet slot unless you don't want to deal with more pets. As other people mentioned, 29 pets are quite a lot to juggle (but who doesn't like their own personal Subetan pet army?). You could always keep your totem locked until you feel inspired to pick which reward you want.