The choice of that to do should always be a personal one you take yourself, but here are some comments from me.
Conventional Jailbreaking wisdom says if you don't have the capability to downgrade then ALWAYS stay on the lowest firmware version available to you as that has the potential for having the most exploits which could be found by jailbreakers.
However, 4.3 is as we know an old OS now, and that conventional wisdom was developed during a period when the devices were less secure and more often exploited. If we are to believe the announcements about the Chronic team and their "5" exploits which are being worked on at the moment, then the best place to move to is actually 5.0 and STAY THERE. Do not accept any security updates which Apple may release in the coming days, weeks, and months.
And of course, CHECK BACK HERE EVERY DAY!. Whenever we get credible news it will be posted along with advice as to what users should do to prepare. We did this for iPad2 users on 4.3 when we clearly told everyone a few days before the Jailbreak was released that they should all move to 4.3.3 immediately. Unfortunately, as you know, not everyone paid attention
So, the choice is yours, but if I was stuck without a JB on iPad2 at the moment, I would move to 5.0 and stay there without accepting any further updates until I saw some credible JB news on the matter.
Hope that helps.