Comhghairdeas ar shaolú bhur mic agus go maire sibh bhur nuacht! "Éanna" is the proper Irish form of the name (it's not unusual for Irish "nn" to become "nd" in Irish words and names borrowed into English and Latin, since it represents a velarised dental n which sounds quite different to the n of other languages). I'm not familiar with the form "Éinde", but it seems a bit spurious. I see that some websites are touting it as an "older spelling", but none of them seem particularly authoritative. It looks to me as if this form may be an attempt to re-gaelicise the anglicised form (such cases are not unheard of). (Even if it were an authentic older spelling, the "nd" would still be pronounced as "nn", as was usual in Old Irish, and the modern form would be "Éinne".) I would definitely go for Éanna -- it's not a particularly obscure name that no one will have heard of (even the Taoiseach of the Republic of Ireland bears it), and those who don't know it will soon learn (it could be a good starting point for proselytising about the Irish language!) Beir bua agus beannacht, agus Doire abú!

Congratulations to you and your wife on your new arrival. Éanna and Éinde are both alternative spellings of the more anglicised 'Enda'. Éinde is an older spelling, I believe. Unless you live in Ireland, you might want to consider whether you are doing your son any favours by giving him a name which could be mistaken for a girl's name, however. That alone is a good reason for choosing the less feminine-looking 'Éinde', in my view.