Optimize SQL Statment

Hello, I have three sql select statments I would like to combine into one.  I have created a statment that works but I am not sure if it is a good solution performance wise.  Is there a better way to run this query?

Thanks Very Much!!

 if exists (Select Top 1 snapsht_id, snpsht_flname, site_url, iWidth, iHeight, isFullPage, fp_flname, fp_iWidth, fp_iHeight
From SiteIndex Where update_freq = 0 and nextupdate < GetDate() Order By nextupdate)
Begin
Select Top 1 snapsht_id, snpsht_flname, site_url, iWidth, iHeight, isFullPage, fp_flname, fp_iWidth, fp_iHeight
From SiteIndex Where update_freq = 0 and nextupdate < GetDate() Order By nextupdate
End
else
if exists (Select Top 1 snapsht_id, snpsht_flname, site_url, iWidth, iHeight, isFullPage, fp_flname, fp_iWidth, fp_iHeight
From SiteIndex Where nextupdate < GetDate() Order By importance desc)
begin
Select Top 1 snapsht_id, snpsht_flname, site_url, iWidth, iHeight, isFullPage, fp_flname, fp_iWidth, fp_iHeight
From SiteIndex Where nextupdate < GetDate() Order By importance desc
end
else
Select Top 1 snapsht_id, snpsht_flname, site_url, iWidth, iHeight, isFullPage, fp_flname, fp_iWidth, fp_iHeight
From SiteIndex Order By nextupdate