SQL performance help: self join or static var

Hi,

Given a table (truncated some real fields for simplicity):

CREATE TABLE city
(  id serial NOT NULL,  muni_city_id integer,  post_code_city_id integer,  alias_city_id integer,  city_type character
varying(15), post_code_type character varying(15),  CONSTRAINT city_pkey PRIMARY KEY (id)
 
)
WITHOUT OIDS;
CREATE INDEX index_city_on_muni_city_id  ON city  USING btree  (muni_city_id);
CREATE INDEX index_city_on_post_code_type  ON city  USING btree  (post_code_type);

Filled with ~168,000 records

Which of the following SQL statements should I expect better 
performance on?

select * from city
where post_code_type in ('P', 'R')

EXPLAIN ANALYZE:
"Seq Scan on city  (cost=0.00..4492.82 rows=76172 width=290) (actual 
time=0.039..163.564 rows=30358 loops=1)"
"  Filter: ((post_code_type)::text = ANY (('{P,R}'::character 
varying[])::text[]))"
"Total runtime: 231.947 ms"

OR

select * from city
where id = muni_city_id

EXPLAIN ANALYZE:
"Seq Scan on city  (cost=0.00..3535.41 rows=383 width=290) (actual 
time=0.022..124.463 rows=30200 loops=1)"
"  Filter: (muni_city_id = id)"
"Total runtime: 195.342 ms"

In my case both statements are semantically equivalent and I'm trying 
to figure out if I should prefer the search of a varchar field for 
static values over the "self join" constraint to an indexed integer 
column?

My (almost completely ignorant) eyes say that the latter 
(id=muni_city_id) is faster by a little - any voices of support or 
other ideas in this regard? Caveats?

Thanks,

Steve