they're both nice areas but I would go for 20th and Wallace...it's a great block, closer to center city and parking is waaay easier there than it is in the other neighborhood you mention.

Being a little biased b/c I live near 20th & Wallace - I like it a little better because you can choose to go to Fairmount or to Center City when dining & other activities - really in the middle of both great choices being on Wallace - it's a great quiet block. Parking is usually not an issue (knocking on wood...). The walk to Center City is quick & easy which is a great draw. Hope this helps & welcome. Phila is no Texas but you already know that - I hope that you enjoy your time here.